Derivatives Derivatives, Volume of Activity (Details)	3 Months Ended
	Mar. 31, 2016 USD ($)
Derivative [Line Items]
Beginning of Period Notional Amount	$ 9,680,000,000
Notional Amount of Derivative Instruments Added	1,000,000,000
Notional Amount of Derivative Instruments Terminated	2,250,000,000
End of Period Notional Amount	8,430,000,000
Interest Rate Swap [Member] | Receive-fixed interest rate swap [Member]
Derivative [Line Items]
Beginning of Period Notional Amount	425,000,000
Notional Amount of Derivative Instruments Added	0
Notional Amount of Derivative Instruments Terminated	0
End of Period Notional Amount	425,000,000
Interest Rate Swap [Member] | Pay-fixed interest rate swap [Member]
Derivative [Line Items]
Beginning of Period Notional Amount	2,955,000,000
Notional Amount of Derivative Instruments Added	1,000,000,000
Notional Amount of Derivative Instruments Terminated	2,250,000,000
End of Period Notional Amount	1,705,000,000
Eurodollar Future [Member]
Derivative [Line Items]
Beginning of Period Notional Amount	6,300,000,000
Notional Amount of Derivative Instruments Added	0
Notional Amount of Derivative Instruments Terminated	0
End of Period Notional Amount	$ 6,300,000,000