Deferred Policy Acquisition Costs and Value of Business Acquired - DAC and VOBA Activity (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Movement Analysis of Deferred Policy Acquisition Costs [Roll Forward]
Beginning balance	$ 2,818.0	$ 3,186.0	$ 3,424.0
Deferrals of commissions and expenses	207.0	234.0	255.0
Amortization:
Amortization, excluding unlocking	(397.0)	(418.0)	(384.0)
Unlocking	(97.0)	(123.0)	(78.0)
Interest accrued	181.0	188.0	193.0
Net amortization included in Consolidated Statements of Operations	(313.0)	(353.0)	(269.0)
Change in unrealized capital gains/losses on available-for-sale securities	586.0	(249.0)	(224.0)
Ending balance	3,298.0	2,818.0	3,186.0
Movement Analysis Of Value of Business Acquired VOBA [Roll Forward]
Beginning balance	556.0	811.0	997.0
Deferrals of commissions and expenses	9.0	8.0	9.0
Amortization, excluding unlocking	(103.0)	(152.0)	(144.0)
Unlocking	(10.0)	(89.0)	(78.0)
Interest accrued	58.0	65.0	76.0
Net amortization included in Consolidated Statements of Operations	(55.0)	(176.0)	(146.0)
Change in unrealized capital gains/losses on available-for-sale securities	308.0	(87.0)	(49.0)
Ending balance	818.0	556.0	811.0
Movement Analysis of Deferred Policy Acquisition Costs and Value of Business Acquired (VOBA) [Roll Forward]
Beginning balance	3,374.0	3,997.0	4,421.0
Deferrals of commissions and expenses	216.0	242.0	264.0
Amortization, excluding unlocking	(500.0)	(570.0)	(528.0)
Unlocking	(107.0)	(212.0)	(156.0)
Interest accrued	239.0	253.0	269.0
Net amortization included in Consolidated Statements of Operations	(368.0)	(529.0)	(415.0)
Change in unrealized capital gains/losses on available-for-sale securities	894.0	(336.0)	(273.0)
Ending balance	4,116.0	3,374.0	3,997.0
Loss Recognition for DAC	0.0	0.0	(3.0)
Loss recognition for VOBA	$ 0.0	$ 0.0	$ (4.0)
Minimum
Movement Analysis of Deferred Policy Acquisition Costs and Value of Business Acquired (VOBA) [Roll Forward]
Rates at which interest accrued	3.50%	4.00%	4.10%
Maximum
Movement Analysis of Deferred Policy Acquisition Costs and Value of Business Acquired (VOBA) [Roll Forward]
Rates at which interest accrued	7.40%	7.40%	7.50%
Guaranteed Minimum Interest Rates
Amortization:
Unlocking	$ (25.0)	$ (80.0)
Movement Analysis Of Value of Business Acquired VOBA [Roll Forward]
Unlocking	$ (26.0)	$ (140.0)