Claim and Claim Adjustment Expense Reserves (Impact of Loss Portfolio Transfer on the Consolidated Statement of Operations) (Details) - Loss Portfolio Transfer - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Liability for Claims and Claims Adjustment Expense [Line Items]
Net A&EP adverse development before consideration of LPT	$ 60	$ 200	$ 150
Retroactive reinsurance benefit recognized	(68)	(107)	(85)
Pretax impact of A&EP reserve development and the LPT	$ (8)	$ 93	$ 65