Fair Value (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Liabilities:
Equity securities held in rabbi trust	$ 15.9	$ 17.2
Other Liabilities [Member]
Liabilities:
Total aggregate costs to date	10.5	11.0
Fair Value, Measurements, Recurring [Member]
Assets:
Derivative assets	19.6	9.3
Equity securities	9.3	9.8
Total assets	28.9	19.1
Liabilities:
Derivative liabilities	1.5	2.9
Total liabilities	1.5	2.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 1 [Member]
Assets:
Derivative assets	0.0	0.0
Equity securities	9.3	9.8
Total assets	9.3	9.8
Liabilities:
Derivative liabilities	0.0	0.0
Total liabilities	0.0	0.0
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 2 [Member]
Assets:
Derivative assets	19.6	9.3
Equity securities	0.0	0.0
Total assets	19.6	9.3
Liabilities:
Derivative liabilities	1.5	2.9
Total liabilities	1.5	2.9
Fair Value, Measurements, Recurring [Member] | Fair Value, Inputs, Level 3 [Member]
Assets:
Derivative assets	0.0	0.0
Equity securities	0.0	0.0
Total assets	0.0	0.0
Liabilities:
Derivative liabilities	0.0	0.0
Total liabilities	$ 0.0	$ 0.0