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, 2017	Dec. 31, 2016
Derivative [Line Items]
Notional Value, Assets	$ 29,819	$ 27,266
Fair Value, Assets	203	427
Notional Value, Liabilities	25,893	19,339
Fair Value, Liabilities	273	249
Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	355	$ 19
Fair Value, Assets	$ 2
Derivative Asset Average Remaining Maturity Period	11 days	11 days
Notional Value, Liabilities	$ 1,369	$ 830
Fair Value, Liabilities	$ 124	$ 106
Derivative Liability Average Remaining Maturity Period	2 years 2 months 27 days	3 years 5 months 1 day
Fair Value Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,650	$ 2,550
Fair Value, Assets	$ 57	$ 49
Derivative Asset Average Remaining Maturity Period	3 years 5 months 1 day	4 years 3 months 11 days
Notional Value, Liabilities	$ 1,250	$ 1,250
Fair Value, Liabilities	$ 11	$ 12
Derivative Liability Average Remaining Maturity Period	1 year 9 months 25 days	2 years 3 months 26 days
Cash Flow Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,272	$ 3,272
Fair Value, Assets	$ 2	$ 108
Derivative Asset Average Remaining Maturity Period	8 years 1 month 16 days	8 years 7 months 17 days
Notional Value, Liabilities	$ 2,007	$ 2,787
Fair Value, Liabilities	$ 9	$ 35
Derivative Liability Average Remaining Maturity Period	6 months 25 days	9 months 29 days
Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets		$ 1,347
Fair Value, Assets		$ 15
Derivative Asset Average Remaining Maturity Period		15 days
Notional Value, Liabilities	$ 158
Fair Value, Liabilities	$ 3
Derivative Liability Average Remaining Maturity Period	15 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,633	$ 6,452
Fair Value, Assets		$ 26
Derivative Asset Average Remaining Maturity Period	8 years 5 months 20 days	11 years 5 months 23 days
Notional Value, Liabilities	$ 5,297	$ 1,561
Fair Value, Liabilities	$ 63	$ 16
Derivative Liability Average Remaining Maturity Period	11 years 5 months 27 days	6 years 6 months 14 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,202	$ 4,705
Fair Value, Assets	$ 10	$ 13
Derivative Asset Average Remaining Maturity Period	4 years 5 months 16 days	6 years 6 months 3 days
Notional Value, Liabilities	$ 4,158	$ 2,320
Fair Value, Liabilities	$ 23	$ 9
Derivative Liability Average Remaining Maturity Period	8 years 5 months 20 days	7 years 9 months 18 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,933	$ 1,748
Fair Value, Assets	$ 13	$ 13
Derivative Asset Average Remaining Maturity Period	26 days	1 month 2 days
Notional Value, Liabilities	$ 2,337	$ 1,722
Fair Value, Liabilities	$ 10	$ 18
Derivative Liability Average Remaining Maturity Period	1 month 9 days	18 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 6,400	$ 2,278
Fair Value, Assets	$ 20	$ 129
Derivative Asset Average Remaining Maturity Period	1 month 9 days	29 days
Notional Value, Liabilities	$ 4,718	$ 4,214
Fair Value, Liabilities	$ 13	$ 43
Derivative Liability Average Remaining Maturity Period	22 days	1 month 2 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 4,225	$ 1,565
Fair Value, Assets	$ 69	$ 43
Derivative Asset Average Remaining Maturity Period	7 years 10 months 6 days	8 years 7 months 6 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,483	$ 1,073
Fair Value, Assets	$ 28	$ 25
Derivative Asset Average Remaining Maturity Period	1 month 6 days	26 days
Notional Value, Liabilities	$ 35	$ 12
Fair Value, Liabilities	$ 1	$ 1
Derivative Liability Average Remaining Maturity Period	1 month 2 days	22 days
Other Economic Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 122	$ 849
Fair Value, Assets	$ 1	$ 6
Derivative Asset Average Remaining Maturity Period	18 days	7 days
Notional Value, Liabilities	$ 750	$ 867
Fair Value, Liabilities	$ 14	$ 6
Derivative Liability Average Remaining Maturity Period	18 days	7 days
Other Economic Hedges [Member] | Equity Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 53	$ 11
Fair Value, Assets	$ 1
Derivative Asset Average Remaining Maturity Period	1 year 2 months 1 day	4 months 24 days
Notional Value, Liabilities	$ 68	$ 102
Fair Value, Liabilities		$ 1
Derivative Liability Average Remaining Maturity Period	11 months 15 days	6 months 25 days
Other Economic Hedges [Member] | Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,491	$ 1,397
Derivative Asset Average Remaining Maturity Period	3 years 7 months 6 days	3 years 4 months 17 days
Notional Value, Liabilities	$ 3,746	$ 3,674
Fair Value, Liabilities	$ 2	$ 2
Derivative Liability Average Remaining Maturity Period	3 years 1 month 13 days	3 years 6 months 25 days