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, 2016	Dec. 31, 2015
Derivative [Line Items]
Notional Value, Assets	$ 27,926	$ 27,442
Fair Value, Assets	635	201
Notional Value, Liabilities	29,569	22,818
Fair Value, Liabilities	700	286
Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	285	$ 36
Fair Value, Assets	$ 2
Derivative Asset Average Remaining Maturity Period	4 days	15 days
Notional Value, Liabilities	$ 997	$ 662
Fair Value, Liabilities	$ 100	$ 64
Derivative Liability Average Remaining Maturity Period	2 years 8 months 5 days	2 years 7 months 6 days
Fair Value Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,800	$ 3,050
Fair Value, Assets	$ 133	$ 73
Derivative Asset Average Remaining Maturity Period	3 years 10 months 21 days	4 years 5 months 5 days
Cash Flow Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 500	$ 1,772
Fair Value, Assets		$ 7
Derivative Asset Average Remaining Maturity Period	1 year 3 months 29 days	9 years 2 months 19 days
Notional Value, Liabilities	$ 6,625	$ 5,009
Fair Value, Liabilities	$ 176	$ 146
Derivative Liability Average Remaining Maturity Period	4 years 9 months 11 days	1 year 1 month 17 days
Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,222	$ 1,140
Fair Value, Assets	$ 8	$ 4
Derivative Asset Average Remaining Maturity Period	18 days	15 days
Notional Value, Liabilities	$ 152
Derivative Liability Average Remaining Maturity Period	18 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 6,952	$ 3,733
Fair Value, Assets	$ 355	$ 42
Derivative Asset Average Remaining Maturity Period	9 years 7 months 2 days	9 years 11 months 23 days
Notional Value, Liabilities	$ 2,475	$ 4,748
Fair Value, Liabilities	$ 10	$ 18
Derivative Liability Average Remaining Maturity Period	10 years 2 months 19 days	10 years 2 months 5 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 47	$ 287
Fair Value, Assets		$ 2
Derivative Asset Average Remaining Maturity Period	7 years 11 months 12 days	9 years 9 months 26 days
Notional Value, Liabilities	$ 4,333	$ 4,158
Fair Value, Liabilities	$ 341	$ 35
Derivative Liability Average Remaining Maturity Period	9 years 2 months 19 days	9 years 11 months 19 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 6,723	$ 3,812
Fair Value, Assets	$ 52	$ 17
Derivative Asset Average Remaining Maturity Period	26 days	26 days
Notional Value, Liabilities	$ 156	$ 452
Fair Value, Liabilities	$ 1	$ 1
Derivative Liability Average Remaining Maturity Period	1 month 13 days	22 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,071	$ 3,201
Fair Value, Assets	$ 12	$ 12
Derivative Asset Average Remaining Maturity Period	1 month 24 days	1 month 2 days
Notional Value, Liabilities	$ 8,048	$ 2,559
Fair Value, Liabilities	$ 43	$ 7
Derivative Liability Average Remaining Maturity Period	1 month 2 days	1 month 13 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 2,200	$ 2,935
Derivative Asset Average Remaining Maturity Period	22 days	22 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,277	$ 3,199
Fair Value, Assets	$ 67	$ 29
Derivative Asset Average Remaining Maturity Period	1 month 6 days	1 month 6 days
Notional Value, Liabilities	$ 20	$ 5
Fair Value, Liabilities	$ 1	$ 1
Derivative Liability Average Remaining Maturity Period	1 month 2 days	29 days
Other Economic Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 372	$ 3,023
Fair Value, Assets	$ 4	$ 13
Derivative Asset Average Remaining Maturity Period	15 days	4 days
Notional Value, Liabilities	$ 3,426	$ 2,380
Fair Value, Liabilities	$ 25	$ 10
Derivative Liability Average Remaining Maturity Period	4 days	11 days
Other Economic Hedges [Member] | Equity Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 64	$ 62
Fair Value, Assets	$ 1
Derivative Asset Average Remaining Maturity Period	8 months 19 days	5 months 19 days
Notional Value, Liabilities	$ 35	$ 24
Fair Value, Liabilities		$ 1
Derivative Liability Average Remaining Maturity Period	3 months 4 days	9 months 26 days
Other Economic Hedges [Member] | Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,413	$ 1,192
Fair Value, Assets	$ 1	$ 2
Derivative Asset Average Remaining Maturity Period	3 years 6 months	2 years 6 months 29 days
Notional Value, Liabilities	$ 3,302	$ 2,821
Fair Value, Liabilities	$ 3	$ 3
Derivative Liability Average Remaining Maturity Period	3 years 22 days	2 years 11 months 27 days