Variable Interest Entities (Details) - USD ($)	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Jan. 10, 2020	Dec. 31, 2018
Variable Interest Entity [Line Items]
Assets	$ 27,465,519,000		$ 26,330,094,000
Liabilities	18,550,147,000		17,287,419,000
Redeemable noncontrolling interests	3,231,846,000		3,071,308,000
Ceded premiums written	755,913,000	$ 635,264,000
Ceded premiums earned	370,864,000	305,219,000
Reinsurance recoverable	2,765,583,000	2,908,343,000	2,791,297,000
Investments in other ventures, under equity method	90,396,000		106,549,000
Vermeer Reinsurance Ltd.
Variable Interest Entity [Line Items]
Redeemable noncontrolling interests	1,021,478,000	605,197,000	1,003,615,000		$ 599,989,000
Variable Interest Entity, Primary Beneficiary | Upsilon RFO Re Ltd.
Variable Interest Entity [Line Items]
Assets	3,400,000,000		3,100,000,000
Liabilities	3,400,000,000		3,100,000,000
Variable Interest Entity, Primary Beneficiary | Upsilon RFO Re Ltd. | Third party investor
Variable Interest Entity [Line Items]
Payments of capital distribution	81,800,000		279,200,000
Variable Interest Entity, Primary Beneficiary | Upsilon RFO Re Ltd. | Third party investor | Non-Voting Preference Shares
Variable Interest Entity [Line Items]
Contributions to subsidiaries	620,900,000		618,700,000
Variable Interest Entity, Primary Beneficiary | Upsilon RFO Re Ltd. | RenaissanceRe Holdings Ltd.
Variable Interest Entity [Line Items]
Payments of capital distribution	$ 29,900,000		$ 31,000,000.0
Variable interest entity, ownership percentage	14.20%		16.50%
Variable Interest Entity, Primary Beneficiary | Upsilon RFO Re Ltd. | RenaissanceRe Holdings Ltd. | Non-Voting Preference Shares
Variable Interest Entity [Line Items]
Contributions to subsidiaries	$ 75,400,000		$ 100,000,000.0
Variable Interest Entity, Primary Beneficiary | Vermeer Reinsurance Ltd.
Variable Interest Entity [Line Items]
Assets	1,000,000,000.0		1,000,000,000.0
Liabilities	27,300,000		23,200,000
Redeemable noncontrolling interests	1,000,000,000.0		1,000,000,000.0
Variable Interest Entity, Not Primary Beneficiary | Renaissance Reinsurance Ltd. | Fibonacci Reinsurance Ltd.
Variable Interest Entity [Line Items]
Ceded premiums written	0	6,000
Ceded premiums earned	0	6,000
Ceded net claims and claim expenses	1,100,000	7,500,000
Reinsurance recoverable	6,400,000		7,500,000
Variable Interest Entity, Not Primary Beneficiary | Mona Lisa Re
Variable Interest Entity [Line Items]
Assets	424,700,000	6,000
Liabilities	424,700,000	6,000
Face amount				$ 400,000,000.0
Variable Interest Entity, Not Primary Beneficiary | Mona Lisa Re | Other investments
Variable Interest Entity [Line Items]
Investment in participating notes	2,900,000
Variable Interest Entity, Not Primary Beneficiary | Mona Lisa Re | DaVinci Reinsurance Ltd.
Variable Interest Entity [Line Items]
Ceded premiums written	7,300,000	0
Ceded premiums earned	1,800,000	0
Variable Interest Entity, Not Primary Beneficiary | Mona Lisa Re | Renaissance Reinsurance Ltd.
Variable Interest Entity [Line Items]
Ceded premiums written	29,200,000	0
Ceded premiums earned	7,300,000	$ 0
Variable Interest Entity, Not Primary Beneficiary | Fibonacci Reinsurance Ltd. | Other investments
Variable Interest Entity [Line Items]
Investment in participating notes	400,000		400,000
Variable Interest Entity, Not Primary Beneficiary | Langhorne Holdings LLC
Variable Interest Entity [Line Items]
Investments in other ventures, under equity method	1,800,000		1,700,000
Variable Interest Entity, Not Primary Beneficiary | Langhorne Partners
Variable Interest Entity [Line Items]
Investments in other ventures, under equity method	$ 100,000		$ 100,000