v3.21.2
Investments - Investments in Funds that are Calculated Using Net Asset Value Per Share (Detail) - USD ($)
$ in Millions
Sep. 30, 2021
Dec. 31, 2020
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Fair Value of Investments $ 3,920  
Cash Instruments Assets [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Fair Value of Investments 3,917 $ 3,664
Cash Instruments Liabilities [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Unfunded Commitments 1,573 1,450
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 2,001 2,042
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 626 557
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 1,547 1,312
Credit Funds [Member] | Cash Instruments Liabilities [Member]    
Fair Value, Investments, Entities That Are Calculated Using Net Asset Value Per Share [Line Items]    
Unfunded Commitments 743 680
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 84 102
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 285 208
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 $ 204 $ 213