Investments - Net Investment Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Gain (Loss) on Investments [Line Items]
Net realized losses on fixed maturity available-for-sale securities	$ (24)		$ (84)
Realized gains on equity securities	(19)		(48)
Change in fair value of other derivatives and embedded derivatives	0		0
Realized losses on other invested assets	3		0
Realized gains (losses) on certain derivative instruments	27		23
Unrealized gains (losses) on certain derivative instruments	135		72
Derivative, Gain (Loss) on Derivative, Net	(3)		(37)
Change In Fair Value Derivatives, Including Other Derivatives	159
Realized gains (losses) on hedging derivatives and reinsurance-related embedded derivatives	159	$ 111	58
Net investment gains (losses)	$ 119		$ (74)
Predecessor
Gain (Loss) on Investments [Line Items]
Net realized losses on fixed maturity available-for-sale securities		3		$ (22)
Realized gains on equity securities		3		3
Change in fair value of other derivatives and embedded derivatives		1		3
Realized losses on other invested assets		0		0
Realized gains (losses) on certain derivative instruments		70		218
Unrealized gains (losses) on certain derivative instruments		48		91
Derivative, Gain (Loss) on Derivative, Net		(8)		(28)
Change In Fair Value Derivatives, Including Other Derivatives		111
Realized gains (losses) on hedging derivatives and reinsurance-related embedded derivatives				284
Net investment gains (losses)		$ 117		$ 265