Notes Payable - Note Issuances (Details) - Notes payable - GBP (£)	Sep. 30, 2022	Jan. 31, 2022	Sep. 30, 2021	Jul. 31, 2021
1.875% Notes due 2027
Debt
Interest rate (as a percent)	1.875%	0.01875%
Principal amount	£ 250,000,000	£ 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%	0.025%
Principal amount	£ 250,000,000	£ 250,000,000
Price of par value (as a percent)	98.445%
Effective yield (as a percent)	2.584%
3.160% Notes due 2030
Debt
Interest rate (as a percent)	3.16%
Principal amount	£ 140,000,000
Price of par value (as a percent)	100.00%
Effective yield (as a percent)	3.16%
3.180% Notes due 2032
Debt
Interest rate (as a percent)	3.18%
Principal amount	£ 345,000,000
Price of par value (as a percent)	100.00%
Effective yield (as a percent)	3.18%
3.390% notes due 2037
Debt
Interest rate (as a percent)	3.39%
Principal amount	£ 115,000,000
Price of par value (as a percent)	100.00%
Effective yield (as a percent)	3.39%
1.125% Notes due 2027
Debt
Interest rate (as a percent)	1.125%		1.125%	0.01125%
Principal amount	£ 400,000,000		£ 400,000,000	£ 400,000,000
Price of par value (as a percent)			99.305%
Effective yield (as a percent)			1.242%
1.750% Notes due 2033
Debt
Interest rate (as a percent)	1.75%		1.75%	0.0175%
Principal amount	£ 350,000,000		£ 350,000,000	£ 350,000,000
Price of par value (as a percent)			99.842%
Effective yield (as a percent)			1.757%