Employee Benefit Plans Investments in nonqualified plans (Details 13) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Nonqualified Defined Benefit and Contribution Plan Investments [Line Items]
Investments in nonqualified benefit plans	$ 105.2	$ 101.4
Equity securities [Member]
Nonqualified Defined Benefit and Contribution Plan Investments [Line Items]
Investments in nonqualified benefit plans	54.2	54.9
Life insurance carried on plan participants [Member]
Nonqualified Defined Benefit and Contribution Plan Investments [Line Items]
Investments in nonqualified benefit plans	34.3	32.8
Other investments [Member]
Nonqualified Defined Benefit and Contribution Plan Investments [Line Items]
Investments in nonqualified benefit plans	$ 16.7	$ 13.7