Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 1,036.4	$ 982.0	$ 817.0
Derivative activity:
Net loss on cash flow hedges	0.0	0.0	(9.5)
Reclassification of net loss on cash flow hedges to income	3.5	3.5	3.5
Changes in employee benefit plan assets and benefit obligations recognized in other comprehensive income:
Net actuarial gain (loss)	43.7	16.3	(23.5)
Curtailment gain	0.0	0.0	1.7
Recognition of prior service credit amortization in income	(0.2)	(0.2)	(0.2)
Recognition of actuarial loss amortization in income	4.6	6.0	5.9
Recognition of settlement cost in income	9.5	2.6	1.0
Total other comprehensive income (loss)	61.1	28.2	(21.1)
Comprehensive income	$ 1,097.5	$ 1,010.2	$ 795.9