Volume of Activity for Interest Rate Derivative Instruments (Details) - Interest Rate Swap - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Notional Value, Beginning of period	$ 8,300,000,000	$ 10,500,000,000
Expirations and terminations	(3,700,000,000)	(2,200,000,000)
Notional Value, End of period	$ 4,600,000,000	$ 8,300,000,000