v3.20.4
Employee Benefit Plans (Presentation Of The Fair Value Of Regions' Qualified Defined-Benefit Pension Plans' Financial Assets) (Details) - USD ($)
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount $ 2,469,000,000 $ 2,299,000,000 $ 2,105,000,000
Collective Investment Trust Funds [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan Assets, Fair Value 671,000,000 665,000,000  
Defined Benefit Plan, Common Collective Trust | Fixed Income Funds [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan Assets, Fair Value 408,000,000 440,000,000  
Defined Benefit Plan, Common Collective Trust | International Fund [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan Assets, Fair Value 46,000,000 47,000,000  
Defined Benefit Plan, Common Collective Trust | Equity Funds      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan Assets, Fair Value 217,000,000 178,000,000  
Fair Value Measured at Net Asset Value Per Share | Real Estate Funds [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan Assets, Fair Value 188,000,000 187,000,000  
Fair Value Measured at Net Asset Value Per Share | Private Equity Funds [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan Assets, Fair Value 280,000,000 101,000,000  
Estimate of Fair Value [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 1,330,000,000 1,346,000,000  
Estimate of Fair Value [Member] | Cash and Cash Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 50,000,000 25,000,000  
Estimate of Fair Value [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 807,000,000 618,000,000  
Estimate of Fair Value [Member] | Fixed Income Securities [Member] | US Treasury and Government [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 299,000,000 481,000,000  
Estimate of Fair Value [Member] | Fixed Income Securities [Member] | Federal Agency Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 18,000,000 26,000,000  
Estimate of Fair Value [Member] | Fixed Income Securities [Member] | Corporate Bond Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 490,000,000 111,000,000  
Estimate of Fair Value [Member] | Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 294,000,000 522,000,000  
Estimate of Fair Value [Member] | Equity Securities [Member] | Domestic [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 130,000,000 346,000,000  
Estimate of Fair Value [Member] | Equity Securities [Member] | International [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 164,000,000 176,000,000  
Estimate of Fair Value [Member] | Mutual Funds [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 179,000,000 181,000,000  
Estimate of Fair Value [Member] | Level 1 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 822,000,000 1,209,000,000  
Estimate of Fair Value [Member] | Level 1 [Member] | Cash and Cash Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 50,000,000 25,000,000  
Estimate of Fair Value [Member] | Level 1 [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 299,000,000 481,000,000  
Estimate of Fair Value [Member] | Level 1 [Member] | Fixed Income Securities [Member] | US Treasury and Government [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 299,000,000 481,000,000  
Estimate of Fair Value [Member] | Level 1 [Member] | Fixed Income Securities [Member] | Federal Agency Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 1 [Member] | Fixed Income Securities [Member] | Corporate Bond Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 1 [Member] | Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 294,000,000 522,000,000  
Estimate of Fair Value [Member] | Level 1 [Member] | Equity Securities [Member] | Domestic [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 130,000,000 346,000,000  
Estimate of Fair Value [Member] | Level 1 [Member] | Equity Securities [Member] | International [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 164,000,000 176,000,000  
Estimate of Fair Value [Member] | Level 1 [Member] | Mutual Funds [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 179,000,000 181,000,000  
Estimate of Fair Value [Member] | Level 2 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 508,000,000 137,000,000  
Estimate of Fair Value [Member] | Level 2 [Member] | Cash and Cash Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 2 [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 508,000,000 137,000,000  
Estimate of Fair Value [Member] | Level 2 [Member] | Fixed Income Securities [Member] | US Treasury and Government [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 2 [Member] | Fixed Income Securities [Member] | Federal Agency Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 18,000,000 26,000,000  
Estimate of Fair Value [Member] | Level 2 [Member] | Fixed Income Securities [Member] | Corporate Bond Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 490,000,000 111,000,000  
Estimate of Fair Value [Member] | Level 2 [Member] | Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 2 [Member] | Equity Securities [Member] | Domestic [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 2 [Member] | Equity Securities [Member] | International [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 2 [Member] | Mutual Funds [Member] | International [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member] | Cash and Cash Equivalents [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member] | Fixed Income Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member] | Fixed Income Securities [Member] | US Treasury and Government [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member] | Fixed Income Securities [Member] | Federal Agency Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member] | Fixed Income Securities [Member] | Corporate Bond Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member] | Equity Securities [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member] | Equity Securities [Member] | Domestic [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member] | Equity Securities [Member] | International [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount 0 0  
Estimate of Fair Value [Member] | Level 3 [Member] | Mutual Funds [Member] | International [Member]      
Defined Benefit Plan Disclosure [Line Items]      
Defined Benefit Plan, Plan Assets, Amount $ 0 $ 0