Retirement Benefit Plans (Analysis of plan assets) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Fair value of plan assets	$ 424.1	$ 423.2
Retirement Plans [Member]
Fair value of plan assets	$ 424.1	$ 422.7	$ 420.6
Percentage of plan assets	100.00%	100.00%
Medical Plan [Member]
Fair value of plan assets	$ 0.0	$ 5.7	$ 7.2
Percentage of plan assets	0.00%	100.00%
Cash and Cash Equivalents [Member]
Fair value of plan assets	$ 3.9	$ 5.7
Cash and Cash Equivalents [Member] | Retirement Plans [Member]
Fair value of plan assets	$ 3.9	$ 5.2
Percentage of plan assets	0.90%	1.20%
Cash and Cash Equivalents [Member] | Medical Plan [Member]
Fair value of plan assets	$ 0.0	$ 5.7
Percentage of plan assets	0.00%	100.00%
Fund Investments [Member]
Fair value of plan assets	$ 207.4	$ 200.6
Fund Investments [Member] | Retirement Plans [Member]
Fair value of plan assets	$ 207.4	$ 200.6
Percentage of plan assets	48.90%	47.40%
Fund Investments [Member] | Medical Plan [Member]
Fair value of plan assets	$ 0.0	$ 0.0
Percentage of plan assets	0.00%	0.00%
Equity Securities [Member]
Fair value of plan assets	$ 122.1	$ 129.1
Equity Securities [Member] | Retirement Plans [Member]
Fair value of plan assets	$ 122.1	$ 129.1
Percentage of plan assets	28.80%	30.50%
Equity Securities [Member] | Medical Plan [Member]
Fair value of plan assets	$ 0.0	$ 0.0
Percentage of plan assets	0.00%	0.00%
Government Debt Securities [Member]
Fair value of plan assets	$ 73.0	$ 70.6
Government Debt Securities [Member] | Retirement Plans [Member]
Fair value of plan assets	$ 73.0	$ 70.6
Percentage of plan assets	17.20%	16.70%
Government Debt Securities [Member] | Medical Plan [Member]
Fair value of plan assets	$ 0.0	$ 0.0
Percentage of plan assets	0.00%	0.00%
Other Assets [Member]
Fair value of plan assets	$ 7.3	$ 5.5
Other Assets [Member] | Retirement Plans [Member]
Fair value of plan assets	$ 7.3	$ 5.5
Percentage of plan assets	1.70%	1.30%
Other Assets [Member] | Medical Plan [Member]
Fair value of plan assets	$ 0.0	$ 0.0
Percentage of plan assets	0.00%	0.00%
Guaranteed Investments Contracts [Member]
Fair value of plan assets	$ 10.4	$ 11.7
Guaranteed Investments Contracts [Member] | Retirement Plans [Member]
Fair value of plan assets	$ 10.4	$ 11.7
Percentage of plan assets	2.50%	2.80%
Guaranteed Investments Contracts [Member] | Medical Plan [Member]
Fair value of plan assets	$ 0.0	$ 0.0
Percentage of plan assets	0.00%	0.00%