Derivative Instruments - Asset and Liability Management Derivative Positions of Company (Detail) - Asset and Liability Management Positions [Member] - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Derivative [Line Items]
Notional Value, Assets	$ 61,578	$ 58,966
Fair Value, Assets	495	142
Notional Value, Liabilities	51,729	42,288
Fair Value, Liabilities	504	301
Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	470	$ 34
Fair Value, Assets	$ 4
Derivative Asset Average Remaining Maturity Period	7 days	3 days
Notional Value, Liabilities	$ 2,258	$ 1,823
Fair Value, Liabilities	$ 144	$ 165
Derivative Liability Average Remaining Maturity Period	1 year 7 months 2 days	2 years 5 months 12 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 12,632	$ 4,408
Derivative Asset Average Remaining Maturity Period	7 years 3 months 10 days	5 years 11 months 26 days
Notional Value, Liabilities	$ 610	$ 5,316
Derivative Liability Average Remaining Maturity Period	20 years 1 month 24 days	13 years 14 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,474	$ 1,259
Derivative Asset Average Remaining Maturity Period	6 years	5 years 8 months 1 day
Notional Value, Liabilities	$ 8,277	$ 4,497
Derivative Liability Average Remaining Maturity Period	5 years 1 month 13 days	6 years 10 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 17,443	$ 5,409
Fair Value, Assets	$ 153	$ 17
Derivative Asset Average Remaining Maturity Period	3 months 25 days	29 days
Notional Value, Liabilities	$ 4,156	$ 5,477
Fair Value, Liabilities	$ 29	$ 11
Derivative Liability Average Remaining Maturity Period	25 days	25 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 10,813	$ 16,333
Fair Value, Assets	$ 47	$ 13
Derivative Asset Average Remaining Maturity Period	14 days	9 months 21 days
Notional Value, Liabilities	$ 27,043	$ 8,113
Fair Value, Liabilities	$ 143	$ 25
Derivative Liability Average Remaining Maturity Period	21 days	10 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,530	$ 10,180
Fair Value, Assets	$ 50	$ 79
Derivative Asset Average Remaining Maturity Period	5 years 4 months 28 days	2 years 11 months 19 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 7,219	$ 1,270
Fair Value, Assets	$ 237	$ 30
Derivative Asset Average Remaining Maturity Period	4 months 17 days	29 days
Notional Value, Liabilities	$ 5,800	$ 4,238
Fair Value, Liabilities	$ 178	$ 81
Derivative Liability Average Remaining Maturity Period	3 years 7 months 6 days	2 years 25 days
Other Economic Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 317	$ 113
Fair Value, Assets	$ 2	$ 1
Derivative Asset Average Remaining Maturity Period	29 days	18 days
Notional Value, Liabilities	$ 248	$ 467
Fair Value, Liabilities	$ 2	$ 6
Derivative Liability Average Remaining Maturity Period	4 months 13 days	14 days
Other Economic Hedges [Member] | Equity Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 49	$ 128
Fair Value, Assets	$ 1	$ 2
Derivative Asset Average Remaining Maturity Period	11 months 8 days	5 months 12 days
Notional Value, Liabilities	$ 87	$ 20
Fair Value, Liabilities	$ 1
Derivative Liability Average Remaining Maturity Period	10 months 24 days	1 year 21 days
Fair Value Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 8,400	$ 18,300
Derivative Asset Average Remaining Maturity Period	2 years 3 months 7 days	3 years 10 months 20 days
Notional Value, Liabilities		$ 4,900
Derivative Liability Average Remaining Maturity Period		3 years 5 months 26 days
Cash Flow Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets		$ 1,532
Derivative Asset Average Remaining Maturity Period		6 years 21 days
Notional Value, Liabilities	$ 3,250	$ 7,150
Fair Value, Liabilities	$ 7	$ 10
Derivative Liability Average Remaining Maturity Period	5 years 1 month 2 days	2 years 1 month 9 days
Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 231
Fair Value, Assets	$ 1
Derivative Asset Average Remaining Maturity Period	18 days
Notional Value, Liabilities		$ 287
Fair Value, Liabilities		$ 3
Derivative Liability Average Remaining Maturity Period		14 days