Pension Plans (Other Plans) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Actual return on pension plan assets	17.00%
Maximize return	56.80%
Liquidity	43.20%
Defined contribution, maximum contribution limit	5.00%
Defined contribution plan, employer contributions	$ 12.6	$ 11.9	$ 11.9
Qualified Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	7.50%	7.50%
Managers’ securities holdings percentage maximum limit of total market value	7.50%
Other Accruals and Payables
Defined Benefit Plan Disclosure [Line Items]
Net pension liability amounts recognized in balance sheet	$ 0.1	$ 0.1