Investments (Activity related to the pretax fixed maturity credit loss component reflected within retained earnings for securities still held for which a portion of an OTTI loss was recognized in OCI) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Other than Temporary Impairment, Credit Losses Recognized in Earnings [Roll Forward]
Balance beginning of period	$ 36	$ 53	$ 62
Reductions for securities sold during the period	(9)	(16)	(9)
Reductions for securities the Company intends to sell or more likely than not will be required to sell	0	(1)	0
Balance end of period	$ 27	$ 36	$ 53