Derivative Instruments - Summary of Notional Amount of Derivatives and Other Financial Instruments (Details) £ in Thousands, $ in Thousands, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2023 CAD ($)	Sep. 30, 2023 GBP (£)	Dec. 31, 2022 CAD ($)	Dec. 31, 2022 GBP (£)	Sep. 30, 2023 GBP (£)	Sep. 30, 2023 USD ($)	Dec. 31, 2022 GBP (£)	Dec. 31, 2022 USD ($)
Designated as Hedging Instrument | Denominated in Canadian Dollars | Net Investment Hedging
Derivatives, Fair Value [Line Items]
Derivative asset	$ 1,725,000		$ 1,075,000
Net investment hedges	250,000		250,000
Designated as Hedging Instrument | Denominated in U.S Dollars | Cash Flow Hedging
Derivatives, Fair Value [Line Items]
Derivative asset						$ 397,601		$ 25,000
Designated as Hedging Instrument | Denominated in U.S Dollars | Fair Value Hedging
Derivatives, Fair Value [Line Items]
Derivative asset						550,000		550,000
Designated as Hedging Instrument | Denominated in Pound Sterling | Net Investment Hedging
Derivatives, Fair Value [Line Items]
Derivative asset | £					£ 1,890,708		£ 1,890,708
Net investment hedges | £		£ 1,050,000		£ 1,050,000
Derivative Instruments Not Designated | Denominated in Canadian Dollars
Derivatives, Fair Value [Line Items]
Derivative asset	$ 80,000		$ 80,000
Derivative Instruments Not Designated | Denominated in U.S Dollars
Derivatives, Fair Value [Line Items]
Derivative asset						$ 0		$ 26,137