Reinsurance (Reinsurance amounts recorded on the Consolidated Statement of Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reinsurance [Abstract]
Direct insurance premiums and fee income	$ 10,269	$ 9,551	$ 9,529
Reinsurance assumed	91	93	73
Reinsurance ceded	(1,485)	(1,413)	(1,311)
Total insurance premiums and fee income	8,875	8,231	8,291
Direct insurance benefits	6,770	6,195	6,420
Reinsurance recoveries netted against benefits	(1,610)	(1,503)	(1,376)
Benefits	$ 5,160	$ 4,692	$ 5,044