v3.20.4
Investments - Cash Instruments by Level (Detail) - USD ($)
$ in Millions
Dec. 31, 2020
Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value $ 82,778 $ 57,827
Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investments in funds at NAV 3,664 4,206
Investment at fair value 79,114 53,621
Level 1 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 47,392 20,125
Level 2 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 15,299 18,214
Level 3 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 16,423 15,282
U.S. [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 43,915 19,094
U.S. [Member] | Level 1 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 43,915 19,094
Non-U.S. [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 2,157 36
Non-U.S. [Member] | Level 1 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 2,109  
Non-U.S. [Member] | Level 2 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 48 36
Corporate debt securities [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 10,991 10,838
Corporate debt securities [Member] | Level 1 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 70 48
Corporate debt securities [Member] | Level 2 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 5,635 7,325
Corporate debt securities [Member] | Level 3 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 5,286 3,465
Securities backed by real estate [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 1,940 2,619
Securities backed by real estate [Member] | Level 2 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 942 2,024
Securities backed by real estate [Member] | Level 3 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 998 595
Money Market Instruments [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 2,185 1,681
Money Market Instruments [Member] | Level 1 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 781 732
Money Market Instruments [Member] | Level 2 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 1,404 949
Other debt obligations [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 497 413
Other debt obligations [Member] | Level 2 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value   94
Other debt obligations [Member] | Level 3 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 497 319
Equity Securities [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 17,429 18,940
Equity Securities [Member] | Level 1 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 517 251
Equity Securities [Member] | Level 2 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value 7,270 7,786
Equity Securities [Member] | Level 3 [Member] | Investments [Member]    
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]    
Investment at fair value $ 9,642 $ 10,903