v3.19.3.a.u2
Income Taxes (Narrative) (Details) - USD ($)
$ in Millions
 12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Income Taxes [Abstract]      
Deferred Tax Liabilities, Net $ 328    
Tax Adjustments, Settlements, and Unusual Provisions $ 131 $ 137 $ 160
Effective Income Tax Rate Reconciliation, at Federal Statutory Income Tax Rate 21.00% 21.00% 35.00%
Deferred Tax Assets, Net   $ 20  
Net Operating Losses And Tax Carryforwards $ 30    
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration 16    
Taxable Temporary Differences That Will Offset Amount Of Gross Deferred Tax Asset 718    
Deferred Tax Assets, Net of Valuation Allowance 461 677  
Decrease in Unrecognized Tax Benefits is Reasonably Possible 28    
Unrecognized Tax Benefits that Would Impact Effective Tax Rate 34 10 $ 21
Income Tax Examination, Penalties and Interest Expense 1 2 2
Income Tax Examination, Penalties and Interest Accrued 1 0  
Investment Tax Credit 59 90 102
Additional Income Tax Expense (Benefit) Recognized due to Tax Reform   37 (61)
Additional Income Tax Expense Recognized related to Revision of Proportional Amortization Calculation associated with Low Income Housing Investments due to Tax Reform     23
Reclassification of the Tax Reform related revaluation of deferred tax items within accumulated other comprehensive income     $ 133
Deferred Tax Assets, Valuation Allowance $ (32) $ (30)