Investments - Net Realized Capital Gains (Details) - USD ($)	3 Months Ended		4 Months Ended	5 Months Ended	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	May 31, 2018	Sep. 30, 2017
Schedule of Investments [Line Items]
Gross gains on sales	$ 6,000,000	$ 28,000,000	$ 7,000,000	$ 49,000,000	$ 141,000,000
Gross losses on sales	(8,000,000)	(7,000,000)	(9,000,000)	(112,000,000)	(47,000,000)
Other than Temporary Impairment Losses, Investments, Portion Recognized in Earnings, Net	0	(1,000,000)	0	0	(14,000,000)
Transactional foreign currency revaluation	9,000,000	3,000,000	16,000,000	(6,000,000)	(11,000,000)
Total net realized capital gains (losses)	(136,000,000)	(33,000,000)	(132,000,000)	(107,000,000)	(61,000,000)
Proceeds from Sale of Available-for-sale Securities	1,100,000,000	1,400,000,000	1,200,000,000	3,500,000,000	5,900,000,000
Other investments
Schedule of Investments [Line Items]
Other, net	(4,000,000)	(2,000,000)	(8,000,000)	(23,000,000)	0
Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(136,000,000)	(58,000,000)	(138,000,000)	(27,000,000)	(139,000,000)
Macro Hedge Program [Member] | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(121,000,000)	(65,000,000)	(121,000,000)	(36,000,000)	(189,000,000)
Variable Annuity [Member]
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(120,000,000)	(50,000,000)	(113,000,000)	(24,000,000)	(136,000,000)
Foreign Exchange Forward [Member] | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(12,000,000)	(4,000,000)	(20,000,000)	7,000,000	4,000,000
Total other non-qualifying derivatives
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives	(4,000,000)		(5,000,000)	(10,000,000)
Total other non-qualifying derivatives | Non-qualifying
Schedule of Investments [Line Items]
Non-qualifying foreign currency derivatives		(4,000,000)			(7,000,000)
Equity Securities [Member]
Schedule of Investments [Line Items]
Marketable Securities	(1,000,000)	0	1,000,000	2,000,000	0
Unrealized Gain (Loss) on Securities	1,000,000		2,000,000	(3,000,000)
Mortgages [Member]
Schedule of Investments [Line Items]
SEC Schedule, 12-09, Valuation Allowances and Reserves, Increase (Decrease) Adjustment	(6,000,000)	0	(6,000,000)	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	$ (1,000,000)	$ 20,000,000	$ (1,000,000)	$ (2,000,000)	$ 81,000,000