Notes Payable - Note Issuances (Details) - Notes payable £ in Millions, $ in Millions	Sep. 30, 2024 USD ($)	Sep. 30, 2024 GBP (£)
4.750% Notes
Debt
Interest rate (as a percent)	4.75%	4.75%
Principal amount	$ 450.0
Price of par value (as a percent)	99.23%	99.23%
Effective yield to maturity (as a percent)	4.923%	4.923%
5.125% Notes
Debt
Interest rate (as a percent)	5.125%	5.125%
Principal amount	$ 800.0
Price of par value (as a percent)	98.91%	98.91%
Effective yield to maturity (as a percent)	5.265%	5.265%
5.375% Notes due 2054
Debt
Interest rate (as a percent)	5.375%	5.375%
Principal amount	$ 500.0
Price of par value (as a percent)	98.37%	98.37%
Effective yield to maturity (as a percent)	5.486%	5.486%
5.000% Notes due 2029
Debt
Interest rate (as a percent)	5.00%	5.00%
Principal amount | £		£ 350.0
Price of par value (as a percent)	99.14%	99.14%
Effective yield to maturity (as a percent)	5.199%	5.199%
5.250% Notes due 2041
Debt
Interest rate (as a percent)	5.25%	5.25%
Principal amount | £		£ 350.0
Price of par value (as a percent)	96.21%	96.21%
Effective yield to maturity (as a percent)	5.601%	5.601%