v3.20.4
Investments - Investments in Funds that are Calculated Using Net Asset Value Per Share (Detail) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Cash Instruments Assets [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Fair Value of Investments $ 3,664 $ 4,206
Cash Instruments Liabilities [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Unfunded Commitments 1,450 1,781
Private Equity Funds [Member] | Cash Instruments Assets [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Fair Value of Investments 2,042 2,767
Private Equity Funds [Member] | Cash Instruments Liabilities [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Unfunded Commitments 557 765
Credit Funds [Member] | Cash Instruments Assets [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Fair Value of Investments 1,312 983
Credit Funds [Member] | Cash Instruments Liabilities [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Unfunded Commitments 680 820
Hedge Funds [Member] | Cash Instruments Assets [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Fair Value of Investments 102 125
Real Estate Funds [Member] | Cash Instruments Assets [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Fair Value of Investments 208 331
Real Estate Funds [Member] | Cash Instruments Liabilities [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Unfunded Commitments $ 213 $ 196