Investments (Components of Net Investment Gains Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Marketable Securities, Gain (Loss)
Fixed maturity securities — net gains (losses) on sales and disposals	$ (25)	$ (28)	$ (60)
Equity securities — net gains (losses) on sales and disposals	26	10	18
Other net investment gains (losses):
Mortgage loans	(9)	5	(11)
Real estate and real estate joint ventures	4	(34)	98
Other limited partnership interests	(11)	(7)	(1)
Other	(4)	11	(2)
Subtotal	(24)	(67)	8
FVO CSEs - changes in estimated fair value:
Commercial mortgage loans	(3)	(2)	(7)
Long-term debt - related to commercial mortgage loans	1	1	4
Non-investment portfolio gains (losses)	(1)	1	0
Subtotal	(3)	0	(3)
Total net investment gains (losses)	(27)	(67)	5
U.S. corporate and foreign corporate
Gain (Loss) on Investments [Line Items]
Total OTTI losses recognized in earnings	0	(16)	(17)
RMBS
Gain (Loss) on Investments [Line Items]
Total OTTI losses recognized in earnings	0	(6)	(14)
State and political subdivision
Gain (Loss) on Investments [Line Items]
Total OTTI losses recognized in earnings	(1)	0	0
Fixed maturity securities
Gain (Loss) on Investments [Line Items]
Total OTTI losses recognized in earnings	(1)	(22)	(31)
Net investment gains (losses)	(26)	(50)	(91)
Industrial
Gain (Loss) on Investments [Line Items]
Total OTTI losses recognized in earnings	0	(16)	(3)
Consumer
Gain (Loss) on Investments [Line Items]
Total OTTI losses recognized in earnings	0	0	(8)
Utility
Gain (Loss) on Investments [Line Items]
Total OTTI losses recognized in earnings	0	0	(6)
Equity securities
Gain (Loss) on Investments [Line Items]
Total OTTI losses recognized in earnings	(4)	(2)	(3)
Net investment gains (losses)	$ 22	$ 8	$ 15