Derivative Instruments - Asset and Liability Management Derivative Positions of Company (Detail) - Asset and Liability Management Positions [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Derivative [Line Items]
Notional Value, Assets	$ 74,796	$ 64,041
Fair Value, Assets	795	449
Notional Value, Liabilities	43,809	54,020
Fair Value, Liabilities	649	548
Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	311	47
Fair Value, Assets	$ 5	$ 1
Derivative Asset Average Remaining Maturity Period	10 days	1 month 9 days
Notional Value, Liabilities	$ 2,096	$ 1,832
Fair Value, Liabilities	$ 172	$ 183
Derivative Liability Average Remaining Maturity Period	1 year 11 months 1 day	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	$ 4,333	$ 11,064
Derivative Asset Average Remaining Maturity Period	4 years 8 months 19 days	7 years 3 months 21 days
Notional Value, Liabilities	$ 6,373	$ 907
Derivative Liability Average Remaining Maturity Period	10 years 10 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	$ 3,379	$ 78
Derivative Asset Average Remaining Maturity Period	4 years 2 months 12 days	13 years 8 months 4 days
Notional Value, Liabilities	$ 4,389	$ 8,538
Derivative Liability Average Remaining Maturity Period	4 years 10 months 6 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	$ 6,044	$ 16,431
Fair Value, Assets	$ 31	$ 73
Derivative Asset Average Remaining Maturity Period	21 days	6 months
Notional Value, Liabilities	$ 11,179	$ 1,925
Fair Value, Liabilities	$ 107	$ 5
Derivative Liability Average Remaining Maturity Period	1 month 6 days	25 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 30,218	$ 10,440
Fair Value, Assets	$ 349	$ 48
Derivative Asset Average Remaining Maturity Period	2 months 8 days	14 days
Notional Value, Liabilities	$ 9,364	$ 28,976
Fair Value, Liabilities	$ 66	$ 157
Derivative Liability Average Remaining Maturity Period	14 days	25 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 18,370	$ 11,610
Fair Value, Assets	$ 290	$ 121
Derivative Asset Average Remaining Maturity Period	3 years 8 months 4 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	$ 4,373	$ 5,073
Fair Value, Assets	$ 109	$ 202
Derivative Asset Average Remaining Maturity Period	1 month 13 days	1 month 17 days
Notional Value, Liabilities	$ 6,740	$ 7,770
Fair Value, Liabilities	$ 300	$ 198
Derivative Liability Average Remaining Maturity Period	2 years 3 months 29 days	2 years 6 months 10 days
Other Economic Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 270	$ 292
Fair Value, Assets	$ 1	$ 1
Derivative Asset Average Remaining Maturity Period	21 days	14 days
Notional Value, Liabilities	$ 344	$ 341
Fair Value, Liabilities	$ 2	$ 2
Derivative Liability Average Remaining Maturity Period	14 days	18 days
Other Economic Hedges [Member] | Equity Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 117	$ 127
Fair Value, Assets		$ 3
Derivative Asset Average Remaining Maturity Period	3 months 29 days	4 months 20 days
Notional Value, Liabilities	$ 74	$ 45
Fair Value, Liabilities	$ 2
Derivative Liability Average Remaining Maturity Period	2 months 8 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	$ 6,600	$ 8,400
Derivative Asset Average Remaining Maturity Period	1 year 11 months 15 days	1 year 9 months 3 days
Fair Value Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Liabilities		$ 100
Derivative Liability Average Remaining Maturity Period		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	$ 3,250	$ 3,250
Derivative Liability Average Remaining Maturity Period	4 years 4 months 2 days	4 years 7 months 2 days
Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 781	$ 479
Fair Value, Assets	$ 10
Derivative Asset Average Remaining Maturity Period	18 days	21 days
Notional Value, Liabilities		$ 336
Fair Value, Liabilities		$ 3
Derivative Liability Average Remaining Maturity Period		21 days