Retirement Benefits (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Net amount of assets (liabilities) of cash, investment income receivable and amounts due to/from brokers, excluded from fair values of pension benefit assets and other benefit assets	$ (0.2)	$ 3.9
Contributions made to 401k retirement benefit plan	111.1	102.5	91.0
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average target allocation for plan assets	45.00%
Fixed Maturity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average target allocation for plan assets	46.00%
All Other Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Weighted-average target allocation for plan assets	9.00%
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated net actuarial loss that will be amortized from accumulated other comprehensive income into net periodic benefit costs over next year	23.8
Estimated prior service credit that will be amortized from accumulated other comprehensive income into net periodic benefit costs over next year	0.8
Accumulated benefit obligation for the defined benefit pension plans	1,908.1	1,758.2
Projected benefit obligation	111.9
Accumulated benefit obligation	109.4
Fair value of plan assets	36.9
Settlement loss	5.2	11.0	13.8
Tax deductible discretionary contributions	3.6	38.6	34.5
Other Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated net actuarial loss that will be amortized from accumulated other comprehensive income into net periodic benefit costs over next year	15.3
Estimated prior service credit that will be amortized from accumulated other comprehensive income into net periodic benefit costs over next year	14.4
Impact on postretirement benefit obligation of one percentage point increase in cost trend	56.7
Impact on service and interest costs of one percentage point increase in cost trend	2.0
Impact on postretirement benefit obligation of one percentage point decrease in cost trend	47.6
Impact on service and interest costs of one percentage point decrease in cost trend	$ 1.8
Other Benefits [Member] | Pre-Medicare [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumed health care cost trend rate to be used for next year to measure expected cost of other benefits	8.00%
Ultimate health care cost trend rate	4.50%
Year in which ultimate trend rate reached	2025
Other Benefits [Member] | Post-Medicare [Member]
Defined Benefit Plan Disclosure [Line Items]
Assumed health care cost trend rate to be used for next year to measure expected cost of other benefits	6.00%
Ultimate health care cost trend rate	4.50%
Year in which ultimate trend rate reached	2021