Fair Value Measurements (excluding Consolidated Investment Entities) - Level 3 Financial Instruments (Details) - Assets measured on recurring basis - Level 3 - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2019	Dec. 31, 2018
Assets held in separate accounts
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		$ 62.0	$ 11.0
Total Realized/Unrealized Gains (Losses) Included in Net income		4.0	1.0
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	0.0
Purchases		78.0	67.0
Issuances		0.0	0.0
Sales		(1.0)	(6.0)
Settlements		0.0	0.0
Transfers into Level 3		3.0	0.0
Transfers out of Level 3		(30.0)	(11.0)
Assets, Fair Value, ending balance	$ 62.0	116.0	62.0
Change In Unrealized Gains (Losses) Included in Earnings		0.0	0.0
Other derivatives, net
Derivatives Rollforward:
Fair Value, Derivatives, beginning balance		0.0	5.0
Total Realized/Unrealized Gains (Losses) Included in Net income			0.0
Total Realized/Unrealized Gains (Losses) Included in OCI			0.0
Purchases			0.0
Issuances			0.0
Sales			0.0
Settlements			(5.0)
Transfers in to Level 3			0.0
Transfers out of Level 3			0.0
Fair Value, Derivatives, ending balance	0.0		0.0
Change in Unrealized Gains (Losses) in Earnings			(5.0)
Other
Derivatives Rollforward:
Fair Value, Derivatives, beginning balance		(44.0)	(147.0)
Total Realized/Unrealized Gains (Losses) Included in Net income		(6.0)	92.0
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	0.0
Purchases		0.0	0.0
Issuances		(9.0)	(5.0)
Sales		0.0	0.0
Settlements		(1.0)	16.0
Transfers in to Level 3		0.0	0.0
Transfers out of Level 3		0.0	0.0
Fair Value, Derivatives, ending balance	(44.0)	(60.0)	(44.0)
Change in Unrealized Gains (Losses) in Earnings		0.0	0.0
U.S. corporate public securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		34.0	48.0
Total Realized/Unrealized Gains (Losses) Included in Net income		(1.0)	0.0
Total Realized/Unrealized Gains (Losses) Included in OCI		(5.0)	1.0
Purchases		5.0	26.0
Issuances		0.0	0.0
Sales		0.0	(13.0)
Settlements		(7.0)	0.0
Transfers into Level 3		38.0	0.0
Transfers out of Level 3		0.0	(26.0)
Assets, Fair Value, ending balance	34.0	74.0	34.0
Change In Unrealized Gains (Losses) Included in Earnings		(1.0)	0.0
U.S. corporate private securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		1,134.0	942.0
Total Realized/Unrealized Gains (Losses) Included in Net income		0.0	5.0
Total Realized/Unrealized Gains (Losses) Included in OCI		(90.0)	48.0
Purchases		342.0	319.0
Issuances		0.0	0.0
Sales		(23.0)	(20.0)
Settlements		(86.0)	(84.0)
Transfers into Level 3		11.0	31.0
Transfers out of Level 3		(11.0)	(11.0)
Assets, Fair Value, ending balance	1,134.0	1,457.0	1,134.0
Change In Unrealized Gains (Losses) Included in Earnings		0.0	0.0
Foreign corporate private securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		217.0	162.0
Total Realized/Unrealized Gains (Losses) Included in Net income		(24.0)	(6.0)
Total Realized/Unrealized Gains (Losses) Included in OCI		(46.0)	(6.0)
Purchases		169.0	134.0
Issuances		0.0	0.0
Sales		(80.0)	(57.0)
Settlements		0.0	(22.0)
Transfers into Level 3		0.0	0.0
Transfers out of Level 3		0.0	0.0
Assets, Fair Value, ending balance	217.0	328.0	217.0
Change In Unrealized Gains (Losses) Included in Earnings		2.0	(13.0)
Residential mortgage-backed securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		28.0	31.0
Total Realized/Unrealized Gains (Losses) Included in Net income		(11.0)	(9.0)
Total Realized/Unrealized Gains (Losses) Included in OCI		(1.0)	0.0
Purchases		13.0	15.0
Issuances		0.0	0.0
Sales		(6.0)	0.0
Settlements		0.0	0.0
Transfers into Level 3		0.0	0.0
Transfers out of Level 3		(2.0)	(9.0)
Assets, Fair Value, ending balance	28.0	23.0	28.0
Change In Unrealized Gains (Losses) Included in Earnings		(7.0)	(9.0)
Commercial mortgage-backed securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		14.0	7.0
Total Realized/Unrealized Gains (Losses) Included in Net income		0.0	0.0
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	0.0
Purchases		0.0	14.0
Issuances		0.0	0.0
Sales		0.0	0.0
Settlements		0.0	0.0
Transfers into Level 3		0.0	0.0
Transfers out of Level 3		(14.0)	(7.0)
Assets, Fair Value, ending balance	14.0	0.0	14.0
Change In Unrealized Gains (Losses) Included in Earnings		0.0	0.0
Other asset-backed securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		127.0	64.0
Total Realized/Unrealized Gains (Losses) Included in Net income		0.0	0.0
Total Realized/Unrealized Gains (Losses) Included in OCI		(1.0)	3.0
Purchases		8.0	67.0
Issuances		0.0	0.0
Sales		0.0	0.0
Settlements		(3.0)	(5.0)
Transfers into Level 3		0.0	29.0
Transfers out of Level 3		(55.0)	(25.0)
Assets, Fair Value, ending balance	127.0	78.0	127.0
Change In Unrealized Gains (Losses) Included in Earnings		0.0	0.0
Fixed maturities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		1,554.0	1,254.0
Total Realized/Unrealized Gains (Losses) Included in Net income		(36.0)	(10.0)
Total Realized/Unrealized Gains (Losses) Included in OCI		(143.0)	46.0
Purchases		537.0	575.0
Issuances		0.0	0.0
Sales		(109.0)	(90.0)
Settlements		(96.0)	(111.0)
Transfers into Level 3		49.0	60.0
Transfers out of Level 3		(82.0)	(78.0)
Assets, Fair Value, ending balance	1,554.0	1,960.0	1,554.0
Change In Unrealized Gains (Losses) Included in Earnings		(6.0)	(22.0)
Equity securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		103.0	87.0
Total Realized/Unrealized Gains (Losses) Included in Net income		(17.0)	(7.0)
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	0.0
Purchases		42.0	25.0
Issuances		0.0	0.0
Sales		0.0	(2.0)
Settlements		0.0	0.0
Transfers into Level 3		0.0	0.0
Transfers out of Level 3		0.0	0.0
Assets, Fair Value, ending balance	103.0	128.0	103.0
Change In Unrealized Gains (Losses) Included in Earnings		(17.0)	(8.0)
Held for sale | Other derivatives, net
Derivatives Rollforward:
Fair Value, Derivatives, beginning balance		83.0	153.0
Total Realized/Unrealized Gains (Losses) Included in Net income		111.0	(65.0)
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	0.0
Purchases		45.0	42.0
Issuances		0.0	0.0
Sales		0.0	0.0
Settlements		(37.0)	(47.0)
Transfers in to Level 3		0.0	0.0
Transfers out of Level 3		0.0	0.0
Fair Value, Derivatives, ending balance	83.0	202.0	83.0
Change in Unrealized Gains (Losses) in Earnings		119.0	(70.0)
Held for sale | IUL
Derivatives Rollforward:
Fair Value, Derivatives, beginning balance		(82.0)	(159.0)
Total Realized/Unrealized Gains (Losses) Included in Net income		(134.0)	69.0
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	0.0
Purchases		0.0	0.0
Issuances		(56.0)	(53.0)
Sales		0.0	0.0
Settlements		55.0	61.0
Transfers in to Level 3		0.0	0.0
Transfers out of Level 3		0.0	0.0
Fair Value, Derivatives, ending balance	(82.0)	(217.0)	(82.0)
Change in Unrealized Gains (Losses) in Earnings		0.0	0.0
Held for sale | U.S. corporate public securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		10.0	9.0
Total Realized/Unrealized Gains (Losses) Included in Net income		0.0	0.0
Total Realized/Unrealized Gains (Losses) Included in OCI		(2.0)	1.0
Purchases		0.0	5.0
Issuances		0.0	0.0
Sales		0.0	3.0
Settlements		(1.0)	0.0
Transfers into Level 3		22.0	0.0
Transfers out of Level 3		(1.0)	0.0
Assets, Fair Value, ending balance	10.0	32.0	10.0
Change In Unrealized Gains (Losses) Included in Earnings	0.0	0.0
Held for sale | U.S. corporate private securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		259.0	185.0
Total Realized/Unrealized Gains (Losses) Included in Net income		0.0	2.0
Total Realized/Unrealized Gains (Losses) Included in OCI		(23.0)	11.0
Purchases		50.0	85.0
Issuances		0.0	0.0
Sales		(2.0)	0.0
Settlements		(15.0)	9.0
Transfers into Level 3		1.0	8.0
Transfers out of Level 3		0.0	1.0
Assets, Fair Value, ending balance	259.0	316.0	259.0
Change In Unrealized Gains (Losses) Included in Earnings	0.0	0.0
Held for sale | Foreign corporate public securities and foreign governments
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		11.0	11.0
Total Realized/Unrealized Gains (Losses) Included in Net income		0.0	0.0
Total Realized/Unrealized Gains (Losses) Included in OCI		4.0	0.0
Purchases		0.0	0.0
Issuances		0.0	0.0
Sales		0.0	0.0
Settlements		0.0	0.0
Transfers into Level 3		0.0	0.0
Transfers out of Level 3		0.0	0.0
Assets, Fair Value, ending balance	11.0	7.0	11.0
Change In Unrealized Gains (Losses) Included in Earnings	0.0	0.0
Held for sale | Foreign corporate private securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		34.0	7.0
Total Realized/Unrealized Gains (Losses) Included in Net income		(4.0)	0.0
Total Realized/Unrealized Gains (Losses) Included in OCI		(11.0)	(2.0)
Purchases		52.0	39.0
Issuances		0.0	0.0
Sales		(13.0)	13.0
Settlements		0.0	(1.0)
Transfers into Level 3		0.0	0.0
Transfers out of Level 3		0.0	0.0
Assets, Fair Value, ending balance	34.0	80.0	34.0
Change In Unrealized Gains (Losses) Included in Earnings	0.0	0.0
Held for sale | Residential mortgage-backed securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		0.0	11.0
Total Realized/Unrealized Gains (Losses) Included in Net income		0.0	0.0
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	0.0
Purchases		0.0	0.0
Issuances		0.0	0.0
Sales		0.0	11.0
Settlements		0.0	0.0
Transfers into Level 3		0.0	0.0
Transfers out of Level 3		0.0	0.0
Assets, Fair Value, ending balance	0.0	0.0	0.0
Change In Unrealized Gains (Losses) Included in Earnings	0.0	0.0
Held for sale | Commercial mortgage-backed securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		0.0	10.0
Total Realized/Unrealized Gains (Losses) Included in Net income		0.0	0.0
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	0.0
Purchases		0.0	0.0
Issuances		0.0	0.0
Sales		0.0	0.0
Settlements		0.0	0.0
Transfers into Level 3		0.0	0.0
Transfers out of Level 3		0.0	10.0
Assets, Fair Value, ending balance	0.0	0.0	0.0
Change In Unrealized Gains (Losses) Included in Earnings	0.0	0.0
Held for sale | Other asset-backed securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		11.0	27.0
Total Realized/Unrealized Gains (Losses) Included in Net income		0.0	0.0
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	1.0
Purchases		0.0	0.0
Issuances		0.0	0.0
Sales		0.0	0.0
Settlements		0.0	0.0
Transfers into Level 3		0.0	6.0
Transfers out of Level 3		(5.0)	21.0
Assets, Fair Value, ending balance	11.0	6.0	11.0
Change In Unrealized Gains (Losses) Included in Earnings	0.0	0.0
Held for sale | Fixed maturities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		325.0	260.0
Total Realized/Unrealized Gains (Losses) Included in Net income		(4.0)	2.0
Total Realized/Unrealized Gains (Losses) Included in OCI		(32.0)	11.0
Purchases		102.0	129.0
Issuances		0.0	0.0
Sales		(15.0)	27.0
Settlements		(16.0)	10.0
Transfers into Level 3		23.0	14.0
Transfers out of Level 3		(6.0)	32.0
Assets, Fair Value, ending balance	325.0	441.0	325.0
Change In Unrealized Gains (Losses) Included in Earnings	0.0	0.0
Held for sale | Equity securities
Fixed Maturities and Equity Securities Rollforward:
Assets, Fair Value, beginning balance		25.0	14.0
Total Realized/Unrealized Gains (Losses) Included in Net income		1.0	(1.0)
Total Realized/Unrealized Gains (Losses) Included in OCI		0.0	0.0
Purchases		7.0	12.0
Issuances		0.0	0.0
Sales		0.0	0.0
Settlements		0.0	0.0
Transfers into Level 3		0.0	0.0
Transfers out of Level 3		0.0	0.0
Assets, Fair Value, ending balance	$ 25.0	33.0	25.0
Change In Unrealized Gains (Losses) Included in Earnings		$ 1.0	$ (1.0)