Derivative Instruments and Hedging Activities - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Derivatives, Fair Value [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 215	$ 304
Additional collateral, independent margin	60	55
Derivative net liability position (less than $1 million)	1	1
Cash collateral from derivatives counterparties	502	544
Securities received from derivatives counterparties, ability to re-pledge	7	172
Cumulative counterparty credit risk valuation adjustment	5	4
Cumulative credit risk valuation adjustment related to our credit quality (less than $1 million)	1	$ 1
Gain (net after-tax) recorded in AOCI related to derivatives designated as cash flow hedges expected to be reclassified to earnings over the next 12 months	$ 173
Maximum length of time over which forecasted transactions were hedged, years	6 years