Derivative Instruments - Asset and Liability Management Derivative Positions of Company (Detail) (Asset and Liability Management Positions [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Notional Value, Assets	$ 24,187	$ 20,217
Fair Value, Assets	323	215
Notional Value, Liabilities	24,108	21,623
Fair Value, Liabilities	476	472
Fair Value Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	3,050	2,750
Fair Value, Assets	95	65
Derivative Asset Average Remaining Maturity Period	5 years 2 months 9 days	5 years 8 months 9 days
Cash Flow Hedges [Member] | Interest Rate Contracts [Member] | Receive Fixed/Pay Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets		250
Derivative Asset Average Remaining Maturity Period		1 month 28 days
Cash Flow Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets	92	272
Fair Value, Assets		6
Derivative Asset Average Remaining Maturity Period	7 years 7 months 2 days	7 years 9 months 4 days
Notional Value, Liabilities	5,888	5,748
Fair Value, Liabilities	285	315
Derivative Liability Average Remaining Maturity Period	1 year 10 months 17 days	1 year 11 months 9 days
Net Investment Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets		1,047
Fair Value, Assets		31
Derivative Asset Average Remaining Maturity Period		15 days
Notional Value, Liabilities	908
Fair Value, Liabilities	14
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	4,115	3,552
Fair Value, Assets	74	14
Derivative Asset Average Remaining Maturity Period	10 years 2 months 19 days	10 years 2 months 19 days
Notional Value, Liabilities		250
Fair Value, Liabilities		1
Derivative Liability Average Remaining Maturity Period		10 years 2 months 19 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Pay Fixed/Receive Floating Swaps [Member]
Derivative [Line Items]
Notional Value, Assets		15
Derivative Asset Average Remaining Maturity Period		10 years 2 months 19 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	6,550	4,839
Fair Value, Assets	62	45
Derivative Asset Average Remaining Maturity Period	29 days	26 days
Notional Value, Liabilities	223	60
Fair Value, Liabilities	3
Derivative Liability Average Remaining Maturity Period	22 days	29 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Futures and Forwards [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	892	448
Fair Value, Assets	18	10
Derivative Asset Average Remaining Maturity Period	1 month 2 days	1 month 17 days
Notional Value, Liabilities	7,993	6,713
Fair Value, Liabilities	61	62
Derivative Liability Average Remaining Maturity Period	1 month 6 days	1 month 2 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Purchased [Member]
Derivative [Line Items]
Notional Value, Assets	2,800	2,500
Derivative Asset Average Remaining Maturity Period	26 days	22 days
Other Economic Hedges [Member] | Interest Rate Contracts [Member] | Options [Member] | Written [Member]
Derivative [Line Items]
Notional Value, Assets	3,690	2,643
Fair Value, Assets	64	31
Derivative Asset Average Remaining Maturity Period	29 days	29 days
Notional Value, Liabilities	5	4
Derivative Liability Average Remaining Maturity Period	1 month 17 days	1 month 10 days
Other Economic Hedges [Member] | Foreign Exchange Forward Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	1,434	510
Fair Value, Assets	5	3
Derivative Asset Average Remaining Maturity Period	7 days	11 days
Notional Value, Liabilities	5,965	6,176
Fair Value, Liabilities	60	41
Derivative Liability Average Remaining Maturity Period	4 days	7 days
Other Economic Hedges [Member] | Equity Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	21	86
Fair Value, Assets		3
Derivative Asset Average Remaining Maturity Period	2 months 19 days	7 months 6 days
Notional Value, Liabilities	68
Derivative Liability Average Remaining Maturity Period	4 months 21 days
Other Economic Hedges [Member] | Credit Contracts [Member]
Derivative [Line Items]
Notional Value, Assets	1,246	1,247
Fair Value, Assets	3	3
Derivative Asset Average Remaining Maturity Period	2 years 10 months 21 days	3 years 3 months 15 days
Notional Value, Liabilities	2,390	2,282
Fair Value, Liabilities	5	5
Derivative Liability Average Remaining Maturity Period	2 years 7 months 24 days	2 years 10 months 6 days
Other Derivatives [Member]
Derivative [Line Items]
Notional Value, Assets	297	58
Fair Value, Assets	2	4
Derivative Asset Average Remaining Maturity Period	11 days	11 days
Notional Value, Liabilities	668	390
Fair Value, Liabilities	$ 48	$ 48
Derivative Liability Average Remaining Maturity Period	1 year 11 months 16 days	3 years 2 months 12 days