Hedging Exposure Future Cash Flows with Interest Rate Swaps For Forecasted Transactions (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2015	Dec. 31, 2014	Jun. 30, 2015	Sep. 30, 2014	Jun. 30, 2014	Dec. 31, 2013
Derivative Instruments Gain Loss [Line Items]
Weighted Average Remaining Term in Months	15 months	16 months
Weighted Average Fixed Interest Rate in Contract	0.94%	1.28%
Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Notional Amount	$ 4,800,000,000	$ 8,300,000,000	$ 5,100,000,000	$ 9,200,000,000	$ 9,900,000,000	$ 10,500,000,000
12 Months or Less
Derivative Instruments Gain Loss [Line Items]
Maturity - lower remaining maturity range	0 months	0 months
Maturity - higher remaining maturity range	12 months	12 months
Weighted Average Remaining Term in Months	7 months	6 months
Weighted Average Fixed Interest Rate in Contract	1.01%	1.73%
12 Months or Less | Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Notional Amount	$ 2,000,000,000	$ 3,700,000,000
Over 12 Months to 24 Months
Derivative Instruments Gain Loss [Line Items]
Maturity - lower remaining maturity range	12 months	12 months
Maturity - higher remaining maturity range	24 months	24 months
Weighted Average Remaining Term in Months	18 months	18 months
Weighted Average Fixed Interest Rate in Contract	0.88%	0.92%
Over 12 Months to 24 Months | Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Notional Amount	$ 2,200,000,000	$ 2,400,000,000
Over 24 Months to 36 Months
Derivative Instruments Gain Loss [Line Items]
Maturity - lower remaining maturity range	24 months	24 months
Maturity - higher remaining maturity range	36 months	36 months
Weighted Average Remaining Term in Months	28 months	29 months
Weighted Average Fixed Interest Rate in Contract	0.95%	0.89%
Over 24 Months to 36 Months | Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Notional Amount	$ 600,000,000	$ 1,800,000,000