Derivatives Derivatives, Volume of Activity (Details)	6 Months Ended
	Jun. 30, 2016 USD ($)
Derivative [Line Items]
Beginning of Period Notional Amount	$ 9,680,000,000
Notional Amount of Derivative Instruments Added	1,250,000,000
Notional Amount of Derivative Instruments Terminated	(2,850,000,000)
End of Period Notional Amount	8,080,000,000
Receive-fixed interest rate swap
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
Pay-fixed interest rate swap
Derivative [Line Items]
Beginning of Period Notional Amount	2,955,000,000
Notional Amount of Derivative Instruments Added	1,250,000,000
Notional Amount of Derivative Instruments Terminated	(2,850,000,000)
End of Period Notional Amount	1,355,000,000	[1]
Eurodollar Future
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
Forward Contracts [Member] | Pay-fixed interest rate swap
Derivative [Line Items]
End of Period Notional Amount	$ 625,000	[1]

[1] The notional amount of pay-fixed interest rate swaps that were forward starting as of June 30, 2016 was $625,000.