Derivative Instruments - Asset and Liability Management Derivative Positions of Company (Detail) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012
Derivative [Line Items]
Fair Value, Assets	$ 1,362	$ 1,546
Fair Value, Liabilities	1,825	2,178
Asset and Liability Management Positions [Member]
Derivative [Line Items]
Notional Value, Assets	22,741	35,234
Fair Value, Assets	284	363
Notional Value, Liabilities	16,715	26,808
Fair Value, Liabilities	706	818
Asset and Liability Management Positions [Member] | Fair Value Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	500	500
Fair Value, Assets	21	30
Derivative Asset Average Remaining Maturity Period	2 years 4 months 2 days	3 years 1 month 2 days
Notional Value, Liabilities
Fair Value, Liabilities
Derivative Liability Average Remaining Maturity Period		0 years
Asset and Liability Management Positions [Member] | Cash Flow Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	7,000	7,000
Fair Value, Assets	31	45
Derivative Asset Average Remaining Maturity Period	1 year 1 month 6 days	1 year 10 months 2 days
Notional Value, Liabilities
Fair Value, Liabilities
Derivative Liability Average Remaining Maturity Period		0 years
Asset and Liability Management Positions [Member] | Cash Flow Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	272	32
Fair Value, Assets	17
Derivative Asset Average Remaining Maturity Period	9 years 7 days	9 years 10 months 17 days
Notional Value, Liabilities	4,288	4,528
Fair Value, Liabilities	548	718
Derivative Liability Average Remaining Maturity Period	2 years 8 months 16 days	3 years 9 months 15 days
Asset and Liability Management Positions [Member] | Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets		758
Fair Value, Assets		1
Derivative Asset Average Remaining Maturity Period		26 days
Notional Value, Liabilities	925
Fair Value, Liabilities	11
Derivative Liability Average Remaining Maturity Period	18 days	0 years
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	3,220	350
Fair Value, Assets	83	1
Derivative Asset Average Remaining Maturity Period	10 years 2 months 23 days	10 years 2 months 16 days
Notional Value, Liabilities		3,775
Fair Value, Liabilities		14
Derivative Liability Average Remaining Maturity Period		10 years 2 months 16 days
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	4,418	11,164
Fair Value, Assets	88	138
Derivative Asset Average Remaining Maturity Period	1 month 2 days	26 days
Notional Value, Liabilities	34	2,921
Fair Value, Liabilities	8	13
Derivative Liability Average Remaining Maturity Period	29 days	15 days
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	41	6,299
Fair Value, Assets	2	18
Derivative Asset Average Remaining Maturity Period	2 months 12 days	1 month 10 days
Notional Value, Liabilities	6,203	12,223
Fair Value, Liabilities	122	57
Derivative Liability Average Remaining Maturity Period	1 month 2 days	1 month 2 days
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	2,325	2,435
Fair Value, Assets
Derivative Asset Average Remaining Maturity Period	26 days	26 days
Notional Value, Liabilities
Fair Value, Liabilities
Derivative Liability Average Remaining Maturity Period		0 years
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	1,800	4,991
Fair Value, Assets	34	123
Derivative Asset Average Remaining Maturity Period	1 month 2 days	1 month 13 days
Notional Value, Liabilities	9	4
Fair Value, Liabilities
Derivative Liability Average Remaining Maturity Period	7 days	22 days
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	1,980	618
Fair Value, Assets	4	4
Derivative Asset Average Remaining Maturity Period	7 days	11 days
Notional Value, Liabilities	2,695	1,383
Fair Value, Liabilities	6	6
Derivative Liability Average Remaining Maturity Period	7 days	4 days
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Equity Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	8	31
Fair Value, Assets
Derivative Asset Average Remaining Maturity Period	1 year 8 months 19 days	2 years 9 months 18 days
Notional Value, Liabilities	66	27
Fair Value, Liabilities
Derivative Liability Average Remaining Maturity Period	1 year 10 months 21 days	2 years 5 months 16 days
Asset and Liability Management Positions [Member] | Other Economic Hedges [Member] | Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	1,177	1,056
Fair Value, Assets	4	3
Derivative Asset Average Remaining Maturity Period	4 years 1 month 13 days	4 years 6 months 22 days
Notional Value, Liabilities	2,495	1,947
Fair Value, Liabilities	$ 11	$ 10
Derivative Liability Average Remaining Maturity Period	4 years 10 months 28 days	3 years 1 month 10 days