Hedging Exposure Future Cash Flows with Interest Rate Swaps For Forecasted Transactions (Details) - USD ($)	3 Months Ended	12 Months Ended
	Mar. 31, 2016	Dec. 31, 2015	Mar. 31, 2015	Dec. 31, 2014
Derivative Instruments Gain Loss [Line Items]
Weighted Average Remaining Term in Months	11 months	12 months
Weighted Average Fixed Interest Rate	0.92%	0.91%
Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Notional Amount	$ 4,000,000,000	$ 4,600,000,000	$ 7,300,000,000	$ 8,300,000,000
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	6 months	6 months
Weighted Average Fixed Interest Rate	0.95%	0.92%
12 Months or Less | Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Notional Amount	$ 2,400,000,000	$ 2,400,000,000
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	17 months	17 months
Weighted Average Fixed Interest Rate	0.87%	0.89%
Over 12 Months to 24 Months | Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Notional Amount	$ 1,600,000,000	$ 1,800,000,000
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	0 months	26 months
Weighted Average Fixed Interest Rate		0.96%
Over 24 Months to 36 Months | Interest Rate Swap
Derivative Instruments Gain Loss [Line Items]
Notional Amount		$ 400,000,000