Employee Benefit Plans Investments in nonqualified plans (Details 12) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Nonqualified Defined Benefit and Contribution Plan Investments [Line Items]
Investments in nonqualified benefit plans	$ 111.0	$ 105.2
Equity securities [Member]
Nonqualified Defined Benefit and Contribution Plan Investments [Line Items]
Investments in nonqualified benefit plans	62.5	54.2
Life insurance carried on plan participants [Member]
Nonqualified Defined Benefit and Contribution Plan Investments [Line Items]
Investments in nonqualified benefit plans	35.5	34.3
Other investments [Member]
Nonqualified Defined Benefit and Contribution Plan Investments [Line Items]
Investments in nonqualified benefit plans	$ 13.0	$ 16.7