Shareholders' Equity - Narrative (Details)											1 Months Ended			12 Months Ended
	Dec. 29, 2023 $ / shares	Dec. 15, 2023 $ / shares	Nov. 01, 2023 shares	Sep. 29, 2023 $ / shares	Sep. 15, 2023 $ / shares	Jun. 30, 2023 $ / shares	Jun. 15, 2023 $ / shares	May 26, 2023 USD ($) $ / shares shares	Mar. 31, 2023 $ / shares	Mar. 15, 2023 $ / shares	Jul. 31, 2021 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	May 31, 2013 USD ($) $ / shares shares	Dec. 31, 2023 USD ($) period director $ / shares shares	Dec. 31, 2022 USD ($) $ / shares shares	Dec. 31, 2021 USD ($)	Aug. 02, 2022 USD ($)	Aug. 11, 2021 USD ($)
Class of Stock [Line Items]
Aggregate authorized shares (in shares) | shares														325,000,000
Authorized common shares (in shares) | shares														225,000,000
Authorized preference shares (in shares) | shares														100,000,000
Par value (in usd per share)														$ 1.00	$ 1.00
Preference shares, issued, value | $														$ 0	$ 0	$ 488,653,000
Preference shares, shares outstanding (in shares) | shares														30,000	30,000
Dividends declared per common share (in usd per share)	$ 0.38	$ 0.38		$ 0.38	$ 0.38		$ 0.38			$ 0.38
Dividends paid per common share (in usd per share)						$ 0.38			$ 0.38
Dividends on preference shares | $														$ 35,375,000	$ 35,375,000	33,266,000
Dividends on common shares | $														$ 75,100,000	$ 64,700,000	$ 67,800,000
Validus
Class of Stock [Line Items]
Shares issued (in shares) | shares			1,322,541
Public Offering
Class of Stock [Line Items]
Sale of stock, number of shares issued (in shares) | shares								7,245,000
Sale of stock, price per share (in usd per share)								$ 192.00
Sale of stock, consideration received on transaction | $								$ 1,352,000,000
Common shares
Class of Stock [Line Items]
Share repurchase program, authorized aggregate amount | $																	$ 500,000,000
Share repurchase program, shares repurchased (in shares) | shares														0
Share repurchase program, remaining authorized amount | $														$ 500,000,000
Series F Preferred Stock
Class of Stock [Line Items]
Sale of stock, number of shares issued (in shares) | shares												10,000
Proceeds from issuance of equity | $												$ 250,000,000
Dividend rate, percentage												5.75%		5.75%
Par value (in usd per share)												$ 1.00
Liquidation preference (in usd per share)												25,000
Liquidation preference per annum (in usd per share)														$ 1,437.5
Quarterly liquidation preference (in usd per share)														$ 359.375
Series F Preferred Stock | Redemption period one
Class of Stock [Line Items]
Redemption price per share (in usd per share)												$ 25,000
Depositary Shares, each representing a 1/1,000th interest in a Series F 5.750% Preference Share, Par Value $1.00 per share
Class of Stock [Line Items]
Sale of stock, number of shares issued (in shares) | shares												10,000,000
Depositary Shares
Class of Stock [Line Items]
Percentage interest in underlying shares											0.10%	0.10%
Depositary Shares | Redemption period one
Class of Stock [Line Items]
Redemption price per share (in usd per share)											$ 25.00	$ 25.00
Series G Preferred Stock
Class of Stock [Line Items]
Sale of stock, number of shares issued (in shares) | shares											20,000
Proceeds from issuance of equity | $											$ 500,000,000
Dividend rate, percentage											4.20%			4.20%
Par value (in usd per share)											$ 1.00
Liquidation preference (in usd per share)											25,000
Liquidation preference per annum (in usd per share)														$ 1,050
Quarterly liquidation preference (in usd per share)														$ 262.50
Series G Preferred Stock | Redemption period one
Class of Stock [Line Items]
Redemption price per share (in usd per share)											$ 25,000
Depositary Shares, each representing a 1/1,000th interest in a Series G 4.20% Preference Share, Par Value $1.00 per share
Class of Stock [Line Items]
Sale of stock, number of shares issued (in shares) | shares											20,000,000
Series C Preferred Stock
Class of Stock [Line Items]
Right to elect directors, required number of dividend periods in arrears | period														6
Right to elect directors, number of directors | director														2
Series E Preferred Stock
Class of Stock [Line Items]
Dividend rate, percentage														5.375%
Par value (in usd per share)													$ 25
Preference shares, issued, value | $													$ 275,000,000
Preference shares, shares issued (in shares) | shares													11,000,000
Preference shares, redemption amount | $																		$ 275,000,000
Preference shares, shares outstanding (in shares) | shares														0
Liquidation preference per annum (in usd per share)														$ 1.34375
Quarterly liquidation preference (in usd per share)														0.3359375
Series F Preferred Shares, Depositary Shares
Class of Stock [Line Items]
Liquidation preference per annum (in usd per share)														1.4375
Quarterly liquidation preference (in usd per share)														0.359375
Series G Preferred Shares, Depositary Shares
Class of Stock [Line Items]
Liquidation preference per annum (in usd per share)														1.05
Quarterly liquidation preference (in usd per share)														$ 0.2625