Investments - Cash Instruments by Level (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in funds at NAV	$ 3,990
Investment at fair value	85,021	$ 82,778
Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investments in funds at NAV	3,988	3,664
Investment at fair value	81,033	79,114
Level 1 [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment at fair value	47,827	47,392
Level 2 [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment at fair value	16,874	15,299
Level 3 [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment at fair value	16,332	16,423
U.S. [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment at fair value	44,531	43,915
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	44,531	43,915
Non-U.S. [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment at fair value	2,096	2,157
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	2,041	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	55	48
Corporate debt securities [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment at fair value	11,217	10,991
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	83	70
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	6,176	5,635
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	4,958	5,286
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	2,213	1,940
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	1,096	942
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	1,117	998
Money Market Instruments [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment at fair value	1,927	2,185
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	766	781
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	1,161	1,404
Other debt obligations [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment at fair value	502	497
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	502	497
Equity Securities [Member] | Investments [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment at fair value	18,547	17,429
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	406	517
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	8,386	7,270
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	$ 9,755	$ 9,642