Earnings Per Common Share (Net Income, Weighted Average Common Shares Used in Calculating Basic Earnings per Common Share and Diluted EPS) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2022	Sep. 30, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Numerator
Net income from continuing operations	$ 68.1	$ 7.3	$ 52.2	$ 149.0	$ 124.0	$ 151.0	$ 187.1	$ 140.8	$ 276.6	$ 602.9	$ 519.4
Less: Net income attributable to non-controlling interest									0.0	0.0	(0.9)
Net income from continuing operations attributable to stockholders									276.6	602.9	518.5
Less: Preferred stock dividends									0.0	(4.7)	(18.7)
Net income from continuing operations attributable to common stockholders, basic									276.6	598.2	499.8
Net income from continuing operations attributable to common stockholders, diluted									276.6	598.2	499.8
Less: Common stock dividends paid									(150.2)	(157.6)	(154.6)
Undistributed earnings, basic									126.4	440.6	345.2
Undistributed earnings, diluted									126.4	440.6	345.2
Add: Net income (loss) from discontinued operations									0.0	758.9	(77.7)
Net income attributable to common stockholders, basic	68.1	7.3	52.2	149.0	120.9	879.8	205.8	150.6	276.6	1,357.1	422.1
Net income attributable to common stockholders, diluted	$ 68.1	$ 7.3	$ 52.2	$ 149.0	$ 120.9	$ 879.8	$ 205.8	$ 150.6	$ 276.6	$ 1,357.1	$ 422.1
Denominator
Weighted average shares outstanding used in basic earnings per share calculations (in shares)									54,371,531	59,140,861	60,114,670
Incremental common shares from:
Weighted average shares used in diluted earnings per share calculations (in shares)									54,782,528	60,123,694	63,179,938
Basic
Distributed earnings - Basic (in dollars per share)									$ 2.76	$ 2.66	$ 2.57
Undistributed earnings - Basic (in dollars per share)									2.33	7.45	5.74
Net income from continuing operations (in dollars per share)	$ 1.27	$ 0.14	$ 0.96	$ 2.67	$ 2.16	$ 2.56	$ 3.07	$ 2.30	5.09	10.11	8.31
Net income (loss) from discontinued operations (in dollars per share)									0	12.84	(1.29)
Net income attributable to common stockholders (in dollars per share)	1.27	0.14	0.96	2.67	2.11	14.88	3.38	2.54	5.09	22.95	7.02
Diluted
Distributed earnings - Diluted (in dollars per share)									2.74	2.62	2.45
Undistributed earnings - Diluted (in dollars per share)									2.31	7.41	5.76
Net income from continuing operations (in dollars per share)	1.27	0.14	0.95	2.65	2.15	2.54	3.05	2.28	5.05	10.03	8.21
Net income (loss) from discontinuing operations (in dollars per share)									0	12.63	(1.23)
Net income attributable to common stockholders (in dollars per share)	$ 1.27	$ 0.14	$ 0.95	$ 2.65	$ 2.09	$ 14.79	$ 3.36	$ 2.51	$ 5.05	$ 22.66	$ 6.98
PSUs
Incremental common shares from:
Incremental common shares from, share-based payment arrangements (in shares)									348,036	403,316	311,712
ESPP
Incremental common shares from:
Incremental common shares from, share-based payment arrangements (in shares)									62,961	45,604	51,631
MCPS
Incremental common shares from:
Incremental common shares from, MCPS (in shares)									0	533,913	2,701,925