Volume of Activity for Interest Rate Derivative Instruments (Details) - Interest Rate Swap - USD ($)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Derivative [Line Items]
Notional Value, Beginning of period	$ 4,600,000,000	$ 8,300,000,000
Expirations and terminations	(600,000,000)	(1,000,000,000)
Notional Value, End of period	$ 4,000,000,000	$ 7,300,000,000