Volume of Activity for Interest Rate Derivative Instruments (Details) - Interest Rate Swap - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Derivative [Line Items]
Notional Value, Beginning of period	$ 5,100,000,000	$ 9,900,000,000	$ 8,300,000,000	$ 10,500,000,000
Expirations and terminations	(300,000,000)	(700,000,000)	(3,500,000,000)	(1,300,000,000)
Notional Value, End of period	$ 4,800,000,000	$ 9,200,000,000	$ 4,800,000,000	$ 9,200,000,000