Hedging Exposure Future Cash Flows with Interest Rate Swaps For Forecasted Transactions (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013
Derivative Instruments, Gain (Loss) [Line Items]
Remaining Term in Months	28 months
Weighted Average Fixed Interest Rate in Contract	1.41%
Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 11,100,000,000
12 Months Or Less
Derivative Instruments, Gain (Loss) [Line Items]
Maturity - remaining maturity range	0 months
Maturity - remaining maturity range	12 months
Remaining Term in Months	7 months
Weighted Average Fixed Interest Rate in Contract	1.90%
12 Months Or Less | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	1,200,000,000
Over 12 Months To 24 Months
Derivative Instruments, Gain (Loss) [Line Items]
Maturity - remaining maturity range	12 months
Maturity - remaining maturity range	24 months
Remaining Term in Months	19 months
Weighted Average Fixed Interest Rate in Contract	1.78%
Over 12 Months To 24 Months | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	3,800,000,000
Over 24 Months To 36 Months
Derivative Instruments, Gain (Loss) [Line Items]
Maturity - remaining maturity range	24 months
Maturity - remaining maturity range	36 months
Remaining Term in Months	30 months
Weighted Average Fixed Interest Rate in Contract	1.30%
Over 24 Months To 36 Months | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	2,700,000,000
Over 36 Months To 48 Months
Derivative Instruments, Gain (Loss) [Line Items]
Maturity - remaining maturity range	36 months
Maturity - remaining maturity range	48 months
Remaining Term in Months	43 months
Weighted Average Fixed Interest Rate in Contract	0.91%
Over 36 Months To 48 Months | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	2,600,000,000
Over 48 Months To 60 Months
Derivative Instruments, Gain (Loss) [Line Items]
Maturity - remaining maturity range	48 months
Maturity - remaining maturity range	60 months
Remaining Term in Months	53 months
Weighted Average Fixed Interest Rate in Contract	0.93%
Over 48 Months To 60 Months | Cash flow hedging
Derivative Instruments, Gain (Loss) [Line Items]
Notional Amount	$ 800,000,000