Notes Payable - Note Issuances (Details) - Notes payable	Apr. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Mar. 31, 2023 GBP (£)	Mar. 31, 2022 GBP (£)	Jan. 31, 2022 GBP (£)
5.050% Notes due 2026
Debt
Interest rate (as a percent)		5.05%	5.05%
Principal amount		$ 500,000,000
Price of par value (as a percent)		99.618%	99.618%
Effective yield (as a percent)		5.189%	5.189%
4.850 Notes due March 2030
Debt
Interest rate (as a percent)		4.85%	4.85%
Principal amount		$ 600,000,000.0
Price of par value (as a percent)		98.813%	98.813%
Effective yield (as a percent)		5.047%	5.047%
1.875% Notes due 2027
Debt
Interest rate (as a percent)		1.875%	1.875%	1.875%	0.01875%
Principal amount | £			£ 250,000,000	£ 250,000,000.0	£ 250,000,000
Price of par value (as a percent)				99.487%
Effective yield (as a percent)				1.974%
2.500% Notes due 2042
Debt
Interest rate (as a percent)		2.50%	2.50%	2.50%	0.025%
Principal amount | £			£ 250,000,000	£ 250,000,000.0	£ 250,000,000
Price of par value (as a percent)				98.445%
Effective yield (as a percent)				2.584%
Senior Unsecured Notes Payable Due December 2028 | Subsequent event
Debt
Interest rate (as a percent)	4.70%
Principal amount	$ 400,000,000.0
Price of par value (as a percent)	9894.90%
Effective yield (as a percent)	4.912%
1.750% notes, issued in July 2021 and due in July 2033 | Subsequent event
Debt
Interest rate (as a percent)	4.90%
Principal amount	$ 600,000,000.0
Price of par value (as a percent)	98.02%
Effective yield (as a percent)	5.148%