Reinsurance (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Share of claims incurred but not reported	$ 4,013.0	$ 4,112.0	$ 6,920.0	$ 7,729.0
Historical Average Claims Ratios, Period, Maximum			10 years
Hollenfels
SEC Schedule, 12-17, Insurance Companies, Reinsurance [Line Items]
Share of incurred and paid claims	$ 756.0	$ 156.0	$ 10,891.0	$ 8,411.0