Asset and Liability Management Derivative Positions of Company (Detail) (Asset And Liability Management Positions [Member], USD $) In Millions, unless otherwise specified	Sep. 30, 2012 Y	Dec. 31, 2011 Y
Fair value hedges | Interest rate contracts | Receive fixed/pay floating swaps
Derivative [Line Items]
Notional Value, Assets	$ 500	$ 500
Fair Value, Assets	30	27
Derivative Asset Average Remaining Maturity Period	3.34	4.09
Fair value hedges | Foreign exchange cross-currency swaps
Derivative [Line Items]
Notional Value, Assets		688
Fair Value, Assets		17
Derivative Asset Average Remaining Maturity Period		5.17
Notional Value, Liabilities		432
Fair Value, Liabilities		23
Derivative Liability Average Remaining Maturity Period		5.17
Cash flow hedges | Interest rate contracts | Receive fixed/pay floating swaps
Derivative [Line Items]
Notional Value, Assets	7,000	750
Fair Value, Assets	51
Derivative Asset Average Remaining Maturity Period	2.10	2.75
Notional Value, Liabilities		6,250
Fair Value, Liabilities		6
Derivative Liability Average Remaining Maturity Period		2.86
Cash flow hedges | Interest rate contracts | Pay fixed/receive floating swaps
Derivative [Line Items]
Notional Value, Liabilities	4,468	4,788
Fair Value, Liabilities	771	803
Derivative Liability Average Remaining Maturity Period	3.96	4.03
Other economic hedges | Interest rate contracts | Receive fixed/pay floating swaps
Derivative [Line Items]
Notional Value, Assets	3,975	2,625
Fair Value, Assets	45	9
Derivative Asset Average Remaining Maturity Period	10.23	10.21
Other economic hedges | Interest rate contracts | Futures and forwards buy
Derivative [Line Items]
Notional Value, Assets	15,159	14,270
Fair Value, Assets	311	150
Derivative Asset Average Remaining Maturity Period	0.08	0.07
Notional Value, Liabilities	107	29
Fair Value, Liabilities	1
Derivative Liability Average Remaining Maturity Period	0.04	0.12
Other economic hedges | Interest rate contracts | Futures and forwards sell
Derivative [Line Items]
Notional Value, Assets	2,720	231
Fair Value, Assets	7	1
Derivative Asset Average Remaining Maturity Period	0.14	0.15
Notional Value, Liabilities	17,673	14,415
Fair Value, Liabilities	389	134
Derivative Liability Average Remaining Maturity Period	0.08	0.11
Other economic hedges | Interest rate contracts | Purchased options
Derivative [Line Items]
Notional Value, Assets	2,250	1,250
Derivative Asset Average Remaining Maturity Period	0.07	0.07
Other economic hedges | Interest rate contracts | Written options
Derivative [Line Items]
Notional Value, Assets	6,097	4,421
Fair Value, Assets	204	80
Derivative Asset Average Remaining Maturity Period	0.12	0.10
Notional Value, Liabilities	8	11
Fair Value, Liabilities	1	1
Derivative Liability Average Remaining Maturity Period	0.19	0.13
Other economic hedges | Foreign exchange forward contracts
Derivative [Line Items]
Notional Value, Assets	1,125	307
Fair Value, Assets	7	1
Derivative Asset Average Remaining Maturity Period	0.02	0.08
Notional Value, Liabilities	1,446	1,414
Fair Value, Liabilities	5	11
Derivative Liability Average Remaining Maturity Period	0.03	0.08
Other economic hedges | Equity contracts
Derivative [Line Items]
Notional Value, Assets	32	54
Fair Value, Assets		1
Derivative Asset Average Remaining Maturity Period	0.53	1.05
Notional Value, Liabilities	33	10
Fair Value, Liabilities	1
Derivative Liability Average Remaining Maturity Period	2.72	0.64
Other economic hedges | Credit contracts
Derivative [Line Items]
Notional Value, Assets	909	800
Fair Value, Assets	3	7
Derivative Asset Average Remaining Maturity Period	4.45	3.71
Notional Value, Liabilities	2,005	1,600
Fair Value, Liabilities	10	8
Derivative Liability Average Remaining Maturity Period	3.28	3.59
Net investment hedges | Foreign exchange forward contracts
Derivative [Line Items]
Notional Value, Assets		708
Fair Value, Assets		$ 4
Derivative Asset Average Remaining Maturity Period		0.08