Investments - Net Realized Capital Gains (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Investments [Line Items]
Gross gains on sales	$ 21	$ 50
Gross losses on sales	(17)	(29)
Marketable Securities	124		$ 0
Transactional foreign currency revaluation	(14)	(18)
Total net realized capital gains (losses)	21	(46)
Gain (Loss) on Investments, Excluding Other than Temporary Impairments	21	(46)
Proceeds from Sale of Available-for-sale Securities	1,100	2,400
Other investments
Schedule of Investments [Line Items]
Other, net	(19)	2
Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	34	(48)
Macro Hedge Program [Member] | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	18	(86)
Variable Annuity [Member]
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	22	(68)
Foreign Currency Swaps and Forwards [Member]
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	17	17
Foreign Currency Swaps and Forwards [Member] | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(3)	(4)
Total other non-qualifying derivatives
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(5)
Total other non-qualifying derivatives | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives		3
Equity Securities [Member]
Schedule of Investments [Line Items]
Marketable Securities	11	0
Accumulated Net Unrealized Investment Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income
Schedule of Investments [Line Items]
Gain (Loss) on Investments, Excluding Other than Temporary Impairments	$ 4	$ 21