Postretirement Benefits Pretax Activity in Accumulated Other Comprehensive Income (Loss) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Net Actuarial Losses [Abstract]
Percentage of benefit obligation or market value of assets, over which actuarial gains and losses are subject to amortization (in hundredths)	10.00%
Pension Plans [Member]
Prior Service Costs (Credits) [Abstract]
Beginning balance	$ 0	$ 0
Prior service credits arising during the period	0	0
Amount recognized as component of net benefit costs	0	0
Ending balance	0	0
Net Actuarial Losses [Abstract]
Beginning balance	441.3	602.1
Actuarial (gains) losses arising during the period	130.2	(139.4)
Amount recognized as component of net benefit costs	(42.9)	(21.4)
Ending balance	528.6	441.3
Total	528.6	441.3
Estimated pretax net actuarial loss in accumulated other comprehensive income (loss) expected to be recognized over the next year	20.0
Other Postretirement Benefit Plans [Member]
Prior Service Costs (Credits) [Abstract]
Beginning balance	(12.5)	(18.2)
Prior service credits arising during the period	0	0
Amount recognized as component of net benefit costs	0.9	5.7
Ending balance	(11.6)	(12.5)
Net Actuarial Losses [Abstract]
Beginning balance	2.3	8.8
Actuarial (gains) losses arising during the period	5.0	(5.2)
Amount recognized as component of net benefit costs	0	(1.3)
Ending balance	7.3	2.3
Total	(4.3)	(10.2)
Estimated pretax prior service (cost) credit in accumulated other comprehensive income (loss) expected to be recognized over the next year	0.7
Estimated pretax net actuarial loss in accumulated other comprehensive income (loss) expected to be recognized over the next year	$ 1.3