Summary of Significant Accounting Policies Losses, Claims and Settlement Expenses - RFIG Run-off (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Supplementary Insurance Information, by Segment
Estimated reduction in beginning reserve	$ 9,471.2	$ 9,237.6	$ 9,206.0
Estimated reduction in ending reserve	9,929.5	9,471.2	9,237.6
RFIG Run-off Business [Member]
Supplementary Insurance Information, by Segment
Estimated reduction in beginning reserve	3.2	19.0	29.6
Total incurred claims and settlement expenses reduced (increased) by changes in estimated rescissions, Current year	0.6	0.9	6.2
Total incurred claims and settlement expenses reduced (increased) by changes in estimated rescissions, Prior year	(0.9)	(12.3)	(3.7)
Total incurred claims and settlement expenses reduced (increased) by changes in estimated rescissions, Sub-total	(0.3)	(11.4)	2.5
Estimated rescission reduction in settled claims	(1.3)	(4.4)	(13.1)
Estimated reduction in ending reserve	$ 1.6	$ 3.2	$ 19.0