Accumulated Other Comprehensive Loss - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Equity [Abstract]
Tax (benefit) expense included in net unrealized gains (losses)	$ (125)	$ (239)	$ 159
Tax included in reclassification	(26)	(18)	(48)
Tax included in amortization	16	15	3
Tax included in reclassification due to accretion	0	0	7
Tax included in reclassification due to closure of VIE	0	0	36
Tax (benefit) expense included in net unrealized gains (losses)	3	(2)	(48)
Tax included in reclassification	6	4	2
Tax (benefit) included in change in unfunded pension postretirement liability	$ 2	$ 0	$ (4)