Accumulated Other Comprehensive Loss - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Equity [Abstract]
Tax (benefit) expense included in net unrealized gains (losses)	$ (65)	$ 2	$ 243	$ (126)
Tax included in reclassification	(6)	(4)	(30)	(26)
Tax included in amortization	4	3	11	10
Tax (benefit) expense included in net unrealized gains (losses)	5	(19)	(33)	(12)
Tax included in reclassification	2	1	5	3
Tax (benefit) included in change in unfunded pension postretirement liability (less than $1 million)	$ 0	$ 0	$ 0	$ 0