Consolidated Statements of Changes in Shareholders' Equity Statement - USD ($) $ in Millions	Total	Serial Preferred Stock	Preferred Shares, No Par Value	Common Shares, $1.00 Par Value	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)	Series B Preferred Stock Serial Preferred Stock	Voting Preference Shares
Common Stock, Dividends, Per Share, Declared	$ 0.20
Balance, Beginning of period at Dec. 31, 2020			$ 493.9	$ 585.2	$ 1,672.9	$ 13,354.9	$ 931.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 2,270.1					2,270.1
Treasury shares purchased				(1.1)	(3.0)	(91.3)
Cash dividends declared on common shares ($0.10, $0.10, $0.20, and $0.20 per share)						(116.8)
Reinvested dividends on restricted stock units					0.8	(0.8)
Net restricted equity awards issued/vested				1.1	(1.1)
Amortization of equity-based compensation					42.7
Other comprehensive income (loss)	(448.5)						(448.5)
Other, net						(15.1)
Balance, End of period at Jun. 30, 2021	$ 18,675.6		493.9	585.2	1,712.3	15,401.0	483.2
Common Stock, Dividends, Per Share, Declared	$ 0.10
Balance, Beginning of period at Mar. 31, 2021			493.9	585.2	1,685.5	14,679.6	392.3
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ 790.1					790.1
Treasury shares purchased				(0.2)	(0.3)	(10.1)
Cash dividends declared on common shares ($0.10, $0.10, $0.20, and $0.20 per share)						(58.4)
Reinvested dividends on restricted stock units					0.4	(0.4)
Net restricted equity awards issued/vested				0.2	(0.2)
Amortization of equity-based compensation					26.9
Other comprehensive income (loss)	90.9						90.9
Other, net						0.2
Balance, End of period at Jun. 30, 2021	$ 18,675.6		493.9	585.2	1,712.3	15,401.0	483.2
Preferred Stock, No Par Value								$ 0
Common Shares, par value (USD per share)	$ 1.00
Preferred Stock, Shares Authorized (shares)		20,000,000.0						500,000	5,000,000.0
Preferred Stock, Shares Issued (shares)								500,000	0
Preferred Stock, No Par Value								$ 0
Common Shares, par value (USD per share)	1.00
Preferred Stock, Shares Authorized (shares)		20,000,000.0						500,000
Preferred Stock, Shares Issued (shares)								500,000
Common Stock, Dividends, Per Share, Declared	$ 0.20
Balance, Beginning of period at Dec. 31, 2021	$ 18,231.6		493.9	584.4	1,772.9	15,339.7	40.7
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	(229.0)					(229.0)
Treasury shares purchased				(0.3)	(0.9)	(28.3)
Cash dividends declared on common shares ($0.10, $0.10, $0.20, and $0.20 per share)						(116.8)
Reinvested dividends on restricted stock units					0.3	(0.3)
Net restricted equity awards issued/vested				0.8	(0.8)
Amortization of equity-based compensation					43.7
Other comprehensive income (loss)	(2,249.7)						(2,249.7)
Other, net						2.4
Balance, End of period at Jun. 30, 2022	$ 15,652.7		493.9	584.9	1,815.2	14,967.7	(2,209.0)
Common Stock, Dividends, Per Share, Declared	$ 0.10
Balance, Beginning of period at Mar. 31, 2022			493.9	584.9	1,788.6	15,569.6	(1,385.8)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income (loss)	$ (542.9)					(542.9)
Treasury shares purchased				0.0	(0.1)	(0.7)
Cash dividends declared on common shares ($0.10, $0.10, $0.20, and $0.20 per share)						(58.4)
Reinvested dividends on restricted stock units					0.3	(0.3)
Net restricted equity awards issued/vested				0.0	0.0
Amortization of equity-based compensation					26.4
Other comprehensive income (loss)	(823.2)						(823.2)
Other, net						0.4
Balance, End of period at Jun. 30, 2022	$ 15,652.7		$ 493.9	$ 584.9	$ 1,815.2	$ 14,967.7	$ (2,209.0)
Preferred Stock, No Par Value								$ 0
Common Shares, par value (USD per share)	$ 1.00
Preferred Stock, Shares Authorized (shares)		20,000,000.0						500,000	5,000,000.0
Preferred Stock, Shares Issued (shares)								500,000	0