Investments - OTTI losses included in AOCI at the time of impairment for fixed income securities (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Investments [Abstract]
Net unrealized gains related to changes in valuation of fixed income securities subsequent to impairment measurement date	$ 208	$ 221
Other-than Impairment Losses Included in Accumulated Other Comprehensive Income
Amount of other-than-temporary impairment losses included in accumulated other comprehensive income for fixed income securities, not included in earnings	(101)	(133)
Municipal
Other-than Impairment Losses Included in Accumulated Other Comprehensive Income
Amount of other-than-temporary impairment losses included in accumulated other comprehensive income for fixed income securities, not included in earnings	(5)	(8)
Corporate
Other-than Impairment Losses Included in Accumulated Other Comprehensive Income
Amount of other-than-temporary impairment losses included in accumulated other comprehensive income for fixed income securities, not included in earnings	0	(7)
ABS
Other-than Impairment Losses Included in Accumulated Other Comprehensive Income
Amount of other-than-temporary impairment losses included in accumulated other comprehensive income for fixed income securities, not included in earnings	(15)	(21)
RMBS
Other-than Impairment Losses Included in Accumulated Other Comprehensive Income
Amount of other-than-temporary impairment losses included in accumulated other comprehensive income for fixed income securities, not included in earnings	(77)	(90)
CMBS
Other-than Impairment Losses Included in Accumulated Other Comprehensive Income
Amount of other-than-temporary impairment losses included in accumulated other comprehensive income for fixed income securities, not included in earnings	$ (4)	$ (7)