Post Retirement Benefit Plans - Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Plan Assets:
Total plan assets	$ 105.9	$ 106.1	$ 139.6
Group BPCE Life
Plan Assets:
Total plan assets	1.3	1.4
Swiss Life Collective BVG Foundation
Plan Assets:
Total plan assets	$ 104.6	104.7
Guaranteed minimum return on mandatory withdrawal portion of fund (as a percent)	1.75%
Guaranteed minimum return on non-mandatory withdrawal portion of fund (as a percent)	1.25%
The Company's percentage of returns above the guaranteed minimum	90.00%
Percentage of returns above the guaranteed minimum to be retained by Swiss Life	10.00%
Swiss Life Collective BVG Foundation | Bonds including cash
Plan Assets:
Target allocation (as a percent)	75.00%
Swiss Life Collective BVG Foundation | Equity Securities
Plan Assets:
Target allocation (as a percent)	5.00%
Swiss Life Collective BVG Foundation | Real estate and mortgages
Plan Assets:
Target allocation (as a percent)	20.00%
Significant Other Observable Inputs (Level 2)
Plan Assets:
Total plan assets	$ 105.9	106.1
Significant Other Observable Inputs (Level 2) | Group BPCE Life
Plan Assets:
Total plan assets	1.3	1.4
Significant Other Observable Inputs (Level 2) | Swiss Life Collective BVG Foundation
Plan Assets:
Total plan assets	$ 104.6	$ 104.7