Derivative Instruments - Notional Amount of Derivatives and Other Financial Instruments (Details) £ in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2023 CAD ($)	Dec. 31, 2023 GBP (£)	Dec. 31, 2022 CAD ($)	Dec. 31, 2022 GBP (£)	Dec. 31, 2023 GBP (£)	Dec. 31, 2023 USD ($)	Dec. 31, 2022 GBP (£)	Dec. 31, 2022 USD ($)
Designated as Hedging Instrument | Net Investment Hedging | Denominated in Canadian Dollars
Derivatives, Fair Value [Line Items]
Derivative asset	$ 2,025,000		$ 1,075,000
Notional amount of non-derivative instruments	250,000		250,000
Designated as Hedging Instrument | Net Investment Hedging | Denominated in Pound Sterling
Derivatives, Fair Value [Line Items]
Derivative asset | £					£ 1,660,708		£ 1,890,708
Notional amount of non-derivative instruments | £		£ 1,050,000		£ 1,050,000
Designated as Hedging Instrument | Cash Flow Hedging | Denominated in U.S. Dollars
Derivatives, Fair Value [Line Items]
Derivative asset						$ 872,601,000		$ 25,000,000
Designated as Hedging Instrument | Fair Value Hedging | Denominated in U.S. Dollars
Derivatives, Fair Value [Line Items]
Derivative asset						550,000,000		550,000,000
Not Designated as Hedging Instrument | Denominated in Canadian Dollars
Derivatives, Fair Value [Line Items]
Derivative asset	$ 80,000		$ 80,000
Not Designated as Hedging Instrument | Denominated in U.S. Dollars
Derivatives, Fair Value [Line Items]
Derivative asset						$ 0		$ 26,137,000