Derivative Instruments - Additional Information (Details) - USD ($) $ in Millions	Dec. 31, 2015	Jul. 31, 2014
Derivatives, Fair Value [Line Items]
Net derivative gain reclassified into earnings within next 12 months	$ 33
Offset asset	20
Offset liability	20
Net derivative assets	36
Net derivative liabilities	5
Fair Value Hedging | Designated as Hedging Instrument | Interest Rate Swap
Derivatives, Fair Value [Line Items]
Derivative liability	$ 2,400	$ 2,400