Retirement Plan (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Defined Contribution Plan, Employer Discretionary Contribution Amount		$ 17.5	$ 17.2	$ 16.1
Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Transition Benefit Costs	$ 11.0			10.8
Defined Benefit Post-retirement Health Coverage [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		1.8
Defined Benefit Plan, Expected Future Benefit Payments, Year Two		1.7
Defined Benefit Plan, Expected Future Benefit Payments, Year Three		1.6
Defined Benefit Plan, Expected Future Benefit Payments, Year Four		1.6
Defined Benefit Plan, Expected Future Benefit Payments, Year Five		1.7
Defined Benefit Plan, Expected Future Benefit Payments, Five Fiscal Years Thereafter		8.3
Retirement Restoration Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Pension expense		0.1	0.1	$ 1.2
Accrued liability		2.7	$ 2.8
Projected benefit obligations under this plan		2.7
Defined Benefit Plan, Expected Future Benefit Payments, Next Twelve Months		$ 0.2