Debt - Summary of Debt (Detail) - USD ($)		Mar. 31, 2024	Dec. 31, 2023	May 31, 2023	Mar. 31, 2023	Mar. 31, 2022	Mar. 31, 2020	Oct. 31, 2018	Mar. 31, 2018	Apr. 30, 2017	Aug. 31, 2016	Jan. 31, 2015	Apr. 30, 2014	Nov. 30, 2002	Mar. 31, 1999
Debt Instrument [Line Items]
Debt	[1]	$ 6,889,700,000	$ 6,888,600,000		$ 6,389,300,000
Fair value		6,297,800,000	6,431,300,000		5,881,000,000
2.45% Senior Notes due 2027 (issued: $500.0, August 2016)
Debt Instrument [Line Items]
Long-term debt		498,700,000	498,600,000		498,300,000
Fair value		468,600,000	468,900,000		464,200,000
Debt, stated interest rate											2.45%
Debt, face amount											$ 500,000,000.0
2.50% Senior Notes due 2027 (issued: $500.0, March 2022)
Debt Instrument [Line Items]
Long-term debt		498,200,000	498,100,000		497,700,000
Fair value		468,500,000	469,100,000		463,800,000
Debt, stated interest rate						2.50%
Debt, face amount						$ 500,000,000.0
6 5/8% Senior Notes due 2029 (issued: $300.0, March 1999)
Debt Instrument [Line Items]
Long-term debt		297,900,000	297,800,000		297,600,000
Fair value		323,500,000	328,700,000		329,600,000
Debt, stated interest rate															6.625%
Debt, face amount															$ 300,000,000.0
4.00% Senior Notes due 2029 (issued: $550.0, October 2018)
Debt Instrument [Line Items]
Long-term debt		547,100,000	546,900,000		546,500,000
Fair value		532,500,000	542,600,000		538,500,000
Debt, stated interest rate								4.00%
Debt, face amount								$ 550,000,000.0
3.20% Senior Notes due 2030 (issued: $500.0, March 2020)
Debt Instrument [Line Items]
Long-term debt		497,400,000	497,300,000		497,000,000.0
Fair value		456,100,000	462,200,000		460,000,000.0
Debt, stated interest rate							3.20%
Debt, face amount							$ 500,000,000.0
3.00% Senior Notes due 2032 (issued: $500.0, March 2022)
Debt Instrument [Line Items]
Long-term debt		496,400,000	496,300,000		496,000,000.0
Fair value		435,700,000	446,000,000.0		446,900,000
Debt, stated interest rate						3.00%
Debt, face amount						$ 500,000,000.0
6.25% Senior Notes due 2032 (issued: $400.0, November 2002)
Debt Instrument [Line Items]
Long-term debt		396,800,000	396,700,000		396,500,000
Fair value		434,200,000	445,600,000		448,100,000
Debt, stated interest rate														6.25%
Debt, face amount														$ 400,000,000.0
4.95% Senior Notes due 2033 (issued: $500.0, May 2023)
Debt Instrument [Line Items]
Long-term debt		496,500,000	496,400,000		0
Fair value		499,200,000	513,000,000.0		0
Debt, stated interest rate				4.95%
Debt, face amount				$ 500,000,000.0
4.35% Senior Notes due 2044 (issued: $350.0, April 2014)
Debt Instrument [Line Items]
Long-term debt		347,000,000.0	347,000,000.0		346,900,000
Fair value		312,800,000	314,200,000		312,300,000
Debt, stated interest rate													4.35%
Debt, face amount													$ 350,000,000.0
3.70% Senior Notes due 2045 (issued: $400.0, January 2015)
Debt Instrument [Line Items]
Long-term debt		395,900,000	395,900,000		395,800,000
Fair value		327,900,000	325,100,000		324,000,000.0
Debt, stated interest rate												3.70%
Debt, face amount												$ 400,000,000.0
4.125% Senior Notes due 2047 (issued: $850.0, April 2017)
Debt Instrument [Line Items]
Long-term debt		842,300,000	842,300,000		842,100,000
Fair value		719,200,000	756,200,000		743,800,000
Debt, stated interest rate										4.125%
Debt, face amount										$ 850,000,000.0
4.20% Senior Notes due 2048 (issued: $600.0, March 2018)
Debt Instrument [Line Items]
Long-term debt		590,700,000	590,600,000		590,400,000
Fair value		519,800,000	534,100,000		530,000,000.0
Debt, stated interest rate									4.20%
Debt, face amount									$ 600,000,000.0
3.95% Senior Notes due 2050 (issued: $500.0, March 2020)
Debt Instrument [Line Items]
Long-term debt		491,200,000	491,100,000		491,000,000.0
Fair value		409,800,000	422,300,000		420,300,000
Debt, stated interest rate							3.95%
Debt, face amount							$ 500,000,000.0
3.70% Senior Notes due 2052 (issued: $500.0, March 2022)
Debt Instrument [Line Items]
Long-term debt		493,600,000	493,600,000		493,500,000
Fair value		$ 390,000,000.0	$ 403,300,000		$ 399,500,000
Debt, stated interest rate						3.70%
Debt, face amount						$ 500,000,000.0

[1] Consists of long-term debt. See Note 4 – Debt for further discussion.