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, 2017	Dec. 31, 2016
Derivative [Line Items]
Notional Value, Assets	$ 29,696	$ 27,266
Fair Value, Assets	188	427
Notional Value, Liabilities	22,202	19,339
Fair Value, Liabilities	300	249
Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	239	$ 19
Fair Value, Assets	$ 1
Derivative Asset Average Remaining Maturity Period	4 days	11 days
Notional Value, Liabilities	$ 1,325	$ 830
Fair Value, Liabilities	$ 124	$ 106
Derivative Liability Average Remaining Maturity Period	2 years 2 months 30 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	$ 3,350	$ 2,550
Fair Value, Assets	$ 42	$ 49
Derivative Asset Average Remaining Maturity Period	3 years 5 months 1 day	4 years 3 months 11 days
Notional Value, Liabilities	$ 1,550	$ 1,250
Fair Value, Liabilities	$ 8	$ 12
Derivative Liability Average Remaining Maturity Period	1 year 3 months 29 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	$ 3,772	$ 3,272
Fair Value, Assets	$ 3	$ 108
Derivative Asset Average Remaining Maturity Period	6 years 10 months 17 days	8 years 7 months 17 days
Notional Value, Liabilities	$ 578	$ 2,787
Fair Value, Liabilities	$ 4	$ 35
Derivative Liability Average Remaining Maturity Period	11 months 23 days	9 months 29 days
Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 347	$ 1,347
Fair Value, Assets	$ 6	$ 15
Derivative Asset Average Remaining Maturity Period	18 days	15 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	$ 3,673	$ 6,452
Fair Value, Assets		$ 26
Derivative Asset Average Remaining Maturity Period	8 years 2 months 19 days	11 years 5 months 23 days
Notional Value, Liabilities	$ 4,328	$ 1,561
Fair Value, Liabilities	$ 94	$ 16
Derivative Liability Average Remaining Maturity Period	12 years 6 months 18 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	$ 2,414	$ 4,705
Fair Value, Assets	$ 15	$ 13
Derivative Asset Average Remaining Maturity Period	3 years 2 months 23 days	6 years 6 months 3 days
Notional Value, Liabilities	$ 4,233	$ 2,320
Fair Value, Liabilities	$ 45	$ 9
Derivative Liability Average Remaining Maturity Period	8 years 2 months 19 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	$ 2,545	$ 1,748
Fair Value, Assets	$ 11	$ 13
Derivative Asset Average Remaining Maturity Period	26 days	1 month 2 days
Notional Value, Liabilities	$ 2,075	$ 1,722
Fair Value, Liabilities	$ 10	$ 18
Derivative Liability Average Remaining Maturity Period	18 days	18 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	$ 5,605	$ 2,278
Fair Value, Assets	$ 12	$ 129
Derivative Asset Average Remaining Maturity Period	11 days	29 days
Notional Value, Liabilities	$ 4,396	$ 4,214
Fair Value, Liabilities	$ 12	$ 43
Derivative Liability Average Remaining Maturity Period	15 days	1 month 2 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	$ 4,005	$ 1,565
Fair Value, Assets	$ 59	$ 43
Derivative Asset Average Remaining Maturity Period	7 years 18 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	$ 1,536	$ 1,073
Fair Value, Assets	$ 28	$ 25
Derivative Asset Average Remaining Maturity Period	1 month 6 days	26 days
Notional Value, Liabilities	$ 21	$ 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	$ 622	$ 849
Fair Value, Assets	$ 9	$ 6
Derivative Asset Average Remaining Maturity Period	18 days	7 days
Notional Value, Liabilities	$ 44	$ 867
Fair Value, Liabilities		$ 6
Derivative Liability Average Remaining Maturity Period	26 days	7 days
Other Economic Hedges [Member] | Equity Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 98	$ 11
Fair Value, Assets	$ 2
Derivative Asset Average Remaining Maturity Period	11 months 26 days	4 months 24 days
Notional Value, Liabilities	$ 27	$ 102
Fair Value, Liabilities		$ 1
Derivative Liability Average Remaining Maturity Period	26 days	6 months 25 days
Other Economic Hedges [Member] | Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	$ 1,490	$ 1,397
Derivative Asset Average Remaining Maturity Period	3 years 7 months 2 days	3 years 4 months 17 days
Notional Value, Liabilities	$ 3,625	$ 3,674
Fair Value, Liabilities	$ 2	$ 2
Derivative Liability Average Remaining Maturity Period	3 years 7 days	3 years 6 months 25 days