Income Taxes - Income Tax Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Income (loss) before income taxes	$ 66.0	$ 149.0	$ 243.0	$ 102.0	$ 126.0	$ 229.0	$ 165.0	$ 8.0	$ 560.0	$ 528.0	$ 385.0
Tax Rate									21.00%	21.00%	35.00%
Income tax expense (benefit) at federal statutory rate									$ 118.0	$ 111.0	$ 135.0
Valuation allowance									(250.0)	(15.0)	(28.0)
Dividend received deduction									(37.0)	(49.0)	(40.0)
Audit settlement									0.0	0.0	0.0
State tax expense (benefit)									1.0	10.0	4.0
Noncontrolling interest									(10.0)	(30.0)	(76.0)
Tax credits									(33.0)	0.0	14.0
Nondeductible expenses									1.0	4.0	2.0
Expirations of federal tax capital loss carryforward									0.0	0.0	2.0
Effect of Tax Reform									0.0	8.0	679.0
Other									5.0	(2.0)	(5.0)
Total income tax expense (benefit)									$ (205.0)	$ 37.0	$ 687.0
Effective tax rate									(36.60%)	7.00%	178.40%
Effect of Tax Reform
Effective Income Tax Rate, Continuing Operations, Tax Rate Reconciliation [Abstract]
Effect of Tax Reform									$ 283.0