Investments - Net Realized Capital Gains (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Schedule of Investments [Line Items]
Gross gains on sales	$ 275	$ 222	$ 219
Gross losses on sales	(113)	(159)	(194)
Net OTTI losses recognized in earnings	(8)	(27)	(41)
Transactional foreign currency revaluation	14	(78)	0
Total net realized capital gains (losses)	165	(110)	(12)
Other investments
Schedule of Investments [Line Items]
Other, net	12	(151)	(8)
Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(6)	74	(7)
Foreign Currency Derivatives | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives		83	13
Total other non-qualifying derivatives | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	8	(9)	(20)
Mortgage loans
Schedule of Investments [Line Items]
Valuation allowances on mortgage loans	$ (1)	$ 0	$ (1)