Accumulated Other Comprehensive Income (Loss) - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Jun. 30, 2015	Jun. 30, 2014
Equity [Abstract]
Tax (benefit) expense included in net unrealized gains (losses)	$ (117)	$ 110	$ (128)	$ 202
Tax included in reclassification	(13)	3	(22)	(6)
Tax included in amortization	(4)	0	7	0
Tax included in reclassification due to accretion	0	1	0	3
Tax (benefit) expense included in net unrealized gains (losses)	19	(10)	7	(23)
Tax included in reclassification	1	1	2	1
Tax (benefit) included in change in unfunded pension postretirement liability (less than $1 million)	$ 0	$ 0	$ 0	$ 0