Debt (Tables)

9 Months Ended

Sep. 30, 2024

Debt Disclosure [Abstract]

Debt Table

Debt at each of the balance sheet periods consisted of:

	September 30, 2024				September 30, 2023				December 31, 2023
(millions)	Carrying Value		Fair Value		Carrying Value		Fair Value		Carrying Value		Fair Value
2.45% Senior Notes due 2027 (issued: $500.0, August 2016)	$	498.9	$	483.2	$	498.5	$	455.8	$	498.6	$	468.9
2.50% Senior Notes due 2027 (issued: $500.0, March 2022)	498.5		482.1		497.9		454.0		498.1		469.1
6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999)	298.1		330.1		297.7		320.8		297.8		328.7
4.00% Senior Notes due 2029 (issued: $550.0, October 2018)	547.3		548.6		546.8		518.9		546.9		542.6
3.20% Senior Notes due 2030 (issued: $500.0, March 2020)	497.6		476.1		497.2		435.1		497.3		462.2
3.00% Senior Notes due 2032 (issued: $500.0, March 2022)	496.6		458.5		496.2		420.5		496.3		446.0
6.25% Senior Notes due 2032 (issued: $400.0, November 2002)	396.9		449.9		396.6		414.3		396.7		445.6
4.95% Senior Notes due 2033 (issued: $500.0, May 2023)	496.7		518.7		496.4		474.7		496.4		513.0
4.35% Senior Notes due 2044 (issued: $350.0, April 2014)	347.0		318.9		347.0		280.9		347.0		314.2
3.70% Senior Notes due 2045 (issued: $400.0, January 2015)	396.0		330.6		395.8		288.2		395.9		325.1
4.125% Senior Notes due 2047 (issued: $850.0, April 2017)	842.4		749.8		842.2		666.3		842.3		756.2
4.20% Senior Notes due 2048 (issued: $600.0, March 2018)	590.8		532.3		590.6		473.3		590.6		534.1
3.95% Senior Notes due 2050 (issued: $500.0, March 2020)	491.3		420.0		491.1		373.5		491.1		422.3
3.70% Senior Notes due 2052 (issued: $500.0, March 2022)	493.7		399.5		493.6		355.8		493.6		403.3
Total	$	6,891.8	$	6,498.3	$	6,887.6	$	5,932.1	$	6,888.6	$	6,431.3