Derivative Instruments - Asset and Liability Management Derivative Positions of Company (Detail) - Asset and Liability Management Positions [Member] - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional Value, Assets	$ 64,143	$ 64,041
Fair Value, Assets	501	449
Notional Value, Liabilities	52,972	54,020
Fair Value, Liabilities	521	548
Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	601	47
Fair Value, Assets	$ 9	$ 1
Derivative Asset Average Remaining Maturity Period	7 days	1 month 9 days
Notional Value, Liabilities	$ 2,386	$ 1,832
Fair Value, Liabilities	$ 147	$ 183
Derivative Liability Average Remaining Maturity Period	1 year 3 months 21 days	2 years 5 months 8 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 4,423	$ 11,064
Derivative Asset Average Remaining Maturity Period	4 years 4 months 17 days	7 years 3 months 21 days
Notional Value, Liabilities	$ 5,690	$ 907
Derivative Liability Average Remaining Maturity Period	10 years 3 months 14 days	23 years 5 months 4 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,006	$ 78
Derivative Asset Average Remaining Maturity Period	4 years 3 months 3 days	13 years 8 months 4 days
Notional Value, Liabilities	$ 4,562	$ 8,538
Derivative Liability Average Remaining Maturity Period	4 years 2 months 26 days	5 years 8 months 1 day
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 5,325	$ 16,431
Fair Value, Assets	$ 29	$ 73
Derivative Asset Average Remaining Maturity Period	25 days	6 months
Notional Value, Liabilities	$ 10,347	$ 1,925
Fair Value, Liabilities	$ 69	$ 5
Derivative Liability Average Remaining Maturity Period	18 days	25 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 28,069	$ 10,440
Fair Value, Assets	$ 139	$ 48
Derivative Asset Average Remaining Maturity Period	3 months 14 days	14 days
Notional Value, Liabilities	$ 17,637	$ 28,976
Fair Value, Liabilities	$ 57	$ 157
Derivative Liability Average Remaining Maturity Period	1 month 20 days	25 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 16,930	$ 11,610
Fair Value, Assets	$ 235	$ 121
Derivative Asset Average Remaining Maturity Period	3 years 4 months 2 days	4 years 1 month 9 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,620	$ 5,073
Fair Value, Assets	$ 78	$ 202
Derivative Asset Average Remaining Maturity Period	1 month 2 days	1 month 17 days
Notional Value, Liabilities	$ 7,541	$ 7,770
Fair Value, Liabilities	$ 241	$ 198
Derivative Liability Average Remaining Maturity Period	2 years 1 month 9 days	2 years 6 months 10 days
Other Economic Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 292	$ 292
Fair Value, Assets	$ 2	$ 1
Derivative Asset Average Remaining Maturity Period	14 days	14 days
Notional Value, Liabilities	$ 275	$ 341
Fair Value, Liabilities	$ 2	$ 2
Derivative Liability Average Remaining Maturity Period	18 days	18 days
Other Economic Hedges [Member] | Equity Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 21	$ 127
Fair Value, Assets	$ 2	$ 3
Derivative Asset Average Remaining Maturity Period	3 months 21 days	4 months 20 days
Notional Value, Liabilities	$ 184	$ 45
Fair Value, Liabilities	$ 5
Derivative Liability Average Remaining Maturity Period	8 months 12 days	5 months 15 days
Fair Value Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 700	$ 8,400
Derivative Asset Average Remaining Maturity Period	14 days	1 year 9 months 3 days
Notional Value, Liabilities	$ 2,250
Derivative Liability Average Remaining Maturity Period	3 years 8 months 12 days
Fair Value Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,330
Derivative Asset Average Remaining Maturity Period	9 years 2 months 23 days
Notional Value, Liabilities	$ 1,850	$ 100
Derivative Liability Average Remaining Maturity Period	8 years 11 months 12 days	9 years 7 months 17 days
Cash Flow Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Liabilities	$ 250	$ 3,250
Derivative Liability Average Remaining Maturity Period	2 months 23 days	4 years 7 months 2 days
Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 826	$ 479
Fair Value, Assets	$ 7
Derivative Asset Average Remaining Maturity Period	21 days	21 days
Notional Value, Liabilities		$ 336
Fair Value, Liabilities		$ 3
Derivative Liability Average Remaining Maturity Period		21 days