Stockholders' Equity - Other Comprehensive Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 30, 2021
Other Comprehensive Income (Loss)
Other comprehensive income (loss), pre-tax	$ (3,093.1)	$ (189.7)	$ (12,410.2)	$ (909.0)
Other comprehensive income (loss), tax	653.3	2.8	2,595.4	142.4
Other comprehensive income (loss)	(2,439.8)	(186.9)	(9,814.8)	(766.6)
Net unrealized gains (losses) on available-for-sale securities including NCI
Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications, pre-tax	(3,653.1)	(546.4)	(14,046.9)	(2,461.6)
Adjustments for assumed changes in amortization patterns, pre-tax	379.8	32.2	1,127.2	121.3
Adjustments for assumed changes in policyholder liabilities, pre-tax	58.9	477.2	510.9	1,573.7
Other comprehensive income (loss), pre-tax	(3,138.1)	(39.6)	(12,325.0)	(770.4)
Other comprehensive income (loss) before reclassifications, tax	778.1	127.4	2,978.5	554.9
Reclassification from accumulated other comprehensive income, tax	(15.6)	0.2	(21.0)	0.2
Adjustments for assumed changes in amortization patterns, tax	(79.8)	(6.8)	(236.7)	(25.5)
Adjustments for assumed changes in policyholder liabilities, tax	(15.7)	(104.8)	(108.5)	(365.3)
Other comprehensive income (loss), tax	667.0	16.0	2,612.3	164.3
Other comprehensive income (loss) before reclassifications, after-tax	(2,875.0)	(419.0)	(11,068.4)	(1,906.7)
Reclassification from accumulated other comprehensive income, after-tax	60.7	(2.4)	62.8	(3.6)
Adjustments for assumed changes in amortization patterns, after-tax	300.0	25.4	890.5	95.8
Adjustments for assumed changes in policyholder liabilities, after-tax	43.2	372.4	402.4	1,208.4
Other comprehensive income (loss)	(2,471.1)	(23.6)	(9,712.7)	(606.1)
Net unrealized gains (losses) on available-for-sale securities including NCI | Net realized capital gains (losses)
Other Comprehensive Income (Loss)
Reclassification from accumulated other comprehensive income, pre-tax	76.3	(2.6)	83.8	(3.8)
Net unrealized gains (losses) on derivative instruments including NCI
Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications, pre-tax	104.6	31.2	84.2	53.7
Reclassification from accumulated other comprehensive income, pre-tax	(4.4)	(3.9)	(21.8)	(13.0)
Adjustments for assumed changes in amortization patterns, pre-tax	(0.7)	(0.5)	4.9	(0.5)
Adjustments for assumed changes in policyholder liabilities, pre-tax	(0.2)	(0.4)	(3.0)	1.0
Other comprehensive income (loss), pre-tax	99.3	26.4	64.3	41.2
Other comprehensive income (loss) before reclassifications, tax	(22.0)	(6.6)	(17.7)	(11.3)
Reclassification from accumulated other comprehensive income, tax	1.0	0.8	4.6	2.7
Adjustments for assumed changes in amortization patterns, tax	0.1	0.1	(1.1)	0.1
Adjustments for assumed changes in policyholder liabilities, tax			0.6	(0.3)
Other comprehensive income (loss), tax	(20.9)	(5.7)	(13.6)	(8.8)
Other comprehensive income (loss) before reclassifications, after-tax	82.6	24.6	66.5	42.4
Reclassification from accumulated other comprehensive income, after-tax	(3.4)	(3.1)	(17.2)	(10.3)
Adjustments for assumed changes in amortization patterns, after-tax	(0.6)	(0.4)	3.8	(0.4)
Adjustments for assumed changes in policyholder liabilities, after-tax	(0.2)	(0.4)	(2.4)	0.7
Other comprehensive income (loss)	78.4	20.7	50.7	32.4
Foreign currency translation adjustment including NCI
Other Comprehensive Income (Loss)
Other comprehensive income (loss), pre-tax	(63.6)	(189.3)	(179.3)	(209.5)
Other comprehensive income (loss), tax	9.5	(4.0)	4.5	(4.6)
Other comprehensive income (loss)	(54.1)	(193.3)	(174.8)	(214.1)
Unrecognized postretirement benefit obligation including NCI
Other Comprehensive Income (Loss)
Other comprehensive income (loss) before reclassifications, pre-tax	0.1		2.2	(9.1)
Other comprehensive income (loss), pre-tax	9.3	12.8	29.8	29.7
Other comprehensive income (loss) before reclassifications, tax	(0.1)		(0.6)	1.9
Reclassification from accumulated other comprehensive income, tax	(2.2)	(3.5)	(7.2)	(10.4)
Other comprehensive income (loss), tax	(2.3)	(3.5)	(7.8)	(8.5)
Other comprehensive income (loss) before reclassifications, after-tax			1.6	(7.2)
Reclassification from accumulated other comprehensive income, after-tax	7.0	9.3	20.4	28.4
Other comprehensive income (loss)	7.0	9.3	22.0	21.2
Unrecognized postretirement benefit obligation including NCI | Operating expense
Other Comprehensive Income (Loss)
Reclassification from accumulated other comprehensive income, pre-tax	$ 9.2	$ 12.8	$ 27.6	$ 38.8