Accumulated Other Comprehensive Income (Loss) - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Equity [Abstract]
Tax (benefit) expense included in net unrealized gains (losses)	$ 2	$ (44)	$ (126)	$ 157
Tax included in reclassification	(4)	(10)	(26)	(16)
Tax included in amortization	(3)	(1)	10	1
Tax included in reclassification due to accretion	0	4	0	7
Tax (benefit) expense included in net unrealized gains (losses)	(19)	(4)	(12)	(28)
Tax included in reclassification	1	1	3	2
Tax (benefit) included in change in unfunded pension postretirement liability (less than $1 million)	$ 0	$ 0	$ 1	$ 0