Common Equity - Stock Options (Details) - Stock options - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Options Activity
Outstanding, shares, beginning balance	3,111,907	2,887,460
Granted, shares		530,612	554,594	476,418
Exercised, shares		(300,657)
Forfeited, shares		(5,508)
Outstanding, shares, ending balance		3,111,907	2,887,460
Options - Weighted Average Exercise Price
Outstanding, Weighted-Average Exercise Price, Beginning	$ 69.84	$ 64.13
Granted, Weighted-Average Exercise Price		91.06
Exercised, Weighted-Average Exercise Price		52.15
Forfeited, Weighted-Average Exercise Price		83.51
Outstanding, Weighted-Average Exercise Price, Ending		$ 69.84	$ 64.13
Options - Additional Disclosures
Outstanding, Weighted-Average Remaining Contractual Life (Years)		6 years 2 months 12 days
Outstanding, Aggregate Intrinsic Value		$ 84.7
Exercisable, shares		1,737,283
Exercisable, Weighted-Average Exercise Price (in dollars per share)		$ 57.88
Exercisable, Weighted-Average Remaining Contractual Life (Years)		4 years 7 months 6 days
Exercisable, Aggregate Intrinsic Value		$ 68.1
Intrinsic value of options exercised		12.9	$ 47.1	$ 62.4
Tax benefit from option exercises		3.5	$ 12.9	$ 17.1
Compensation cost not yet recognized		$ 2.6
Weighted-average period over which unrecognized compensation cost is expected to be recognized		1 year 7 months 6 days
Estimated weighted-average fair value per stock option (in dollars per share)		$ 13.20	$ 10.94	$ 8.60
Subsequent event
Options Activity
Granted, shares	437,269
Options - Weighted Average Exercise Price
Granted, Weighted-Average Exercise Price	$ 96.04
Options - Additional Disclosures
Estimated weighted-average fair value per stock option (in dollars per share)	$ 14.71