Investments - Net Realized Capital Gains (Details) - USD ($)	1 Months Ended	2 Months Ended	3 Months Ended	5 Months Ended	6 Months Ended
	Jun. 30, 2018	May 31, 2018	Jun. 30, 2017	May 31, 2018	Jun. 30, 2017
Schedule of Investments [Line Items]
Gross gains on sales	$ 1,000,000	$ 28,000,000	$ 63,000,000	$ 49,000,000	$ 113,000,000
Gross losses on sales	(1,000,000)	(95,000,000)	(11,000,000)	(112,000,000)	(40,000,000)
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0	(13,000,000)	0	(13,000,000)
Transactional foreign currency revaluation	7,000,000	8,000,000	4,000,000	(6,000,000)	(14,000,000)
Total net realized capital gains (losses)	4,000,000	(128,000,000)	18,000,000	(107,000,000)	(28,000,000)
Proceeds from Sale of Available-for-sale Securities	100,000,000	2,400,000,000	2,100,000,000	3,500,000,000	4,500,000,000
Other investments
Schedule of Investments [Line Items]
Other, net	(4,000,000)	(4,000,000)	0	(23,000,000)	2,000,000
Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(2,000,000)	(61,000,000)	(32,000,000)	(27,000,000)	(81,000,000)
Foreign Exchange Forward [Member] | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(8,000,000)	(10,000,000)	(9,000,000)	7,000,000	8,000,000
Macro Hedge Program [Member] | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	0	(54,000,000)	(38,000,000)	(36,000,000)	(124,000,000)
Variable Annuity [Member]
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	7,000,000	(46,000,000)	(18,000,000)	(24,000,000)	(86,000,000)
Total other non-qualifying derivatives
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(1,000,000)	(5,000,000)		(10,000,000)
Total other non-qualifying derivatives | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives			(5,000,000)		(3,000,000)
Equity Securities [Member]
Schedule of Investments [Line Items]
Marketable Securities	2,000,000	(9,000,000)	0	2,000,000	0
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	0	0	0	0
Unrealized Gain (Loss) on Securities	0	(6,000,000)		(8,000,000)
Mortgages [Member]
Schedule of Investments [Line Items]
Valuation Allowances and Reserves, Additions for Adjustments	0	0	2,000,000	0	2,000,000
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	$ 0	$ (6,000,000)	$ 39,000,000	$ (2,000,000)	$ 60,000,000