Benefit Plans Benefit Plans - Allocation of Plan Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Acquired benefit plans	$ 625.1	$ 0.0
Target Allocation	100.00%
Actual Allocation	100.00%	100.00%
Fair value of plan assets	$ 834.6	$ 347.9	$ 364.2
Fair value of plan assets at end of year		347.9
Pension Benefits | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	248.6
Fair value of plan assets at end of year		82.2
Pension Benefits | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	308.0
Fair value of plan assets at end of year		212.4
Pension Benefits | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	278.0
Fair value of plan assets at end of year		53.3
Pension Benefits | Other Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	229.9
Pension Benefits | Other Alternative Investments [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0
Pension Benefits | Other Alternative Investments [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0
Pension Benefits | Other Alternative Investments [Member] | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	229.9
Pension Benefits | Other common collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	148.4	143.4
Pension Benefits | Other common collective trusts | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	148.4	143.4
Pension Benefits | US Treasury and Government [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7.7	3.3
Pension Benefits | US Treasury and Government [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	7.7	3.3
Pension Benefits | Cash and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	95.7	3.4
Pension Benefits | Cash and other | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	95.7	3.4
Pension Benefits | Money Market Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	89.8	14.7
Pension Benefits | Money Market Funds [Member] | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	89.8	14.7
Pension Benefits | Other Debt Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.9	0.5
Pension Benefits | Other Debt Obligations [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	6.9	0.5
Pension Benefits | Foreign Government Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.5	17.8
Pension Benefits | Foreign Government Debt Securities [Member] | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.5	17.8
Pension Benefits | International corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	77.3
Pension Benefits | International corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	77.3
Pension Benefits | U.S. corporate bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	44.8	47.4
Pension Benefits | U.S. corporate bonds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	44.8	47.4
Pension Benefits | Multi-strategy hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20.4	17.2
Pension Benefits | Multi-strategy hedge funds | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.1
Pension Benefits | Multi-strategy hedge funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	18.3	17.2
Pension Benefits | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11.7	16.5
Pension Benefits | Private equity funds | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	11.7	16.5
Pension Benefits | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	22.4	19.6
Pension Benefits | Real estate | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.3
Pension Benefits | Real estate | Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 18.1	$ 19.6
Equity securities | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	45.00%
Actual Allocation	45.00%	45.00%
Debt securities | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	40.00%
Actual Allocation	41.00%	39.00%
Real estate | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	5.00%
Actual Allocation	5.00%	6.00%
Other | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Target Allocation	10.00%
Actual Allocation	9.00%	10.00%
U.S. small cap core | Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 16.9	$ 16.9
U.S. small cap core | Pension Benefits | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.9	16.9
U.S. mid cap value | Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	13.2
U.S. mid cap value | Pension Benefits | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	13.2
International developed markets | Pension Benefits | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	46.1	34.0
International developed markets | Pension Benefits | Equity securities | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 46.1	$ 34.0
Special Situation Private Equity and Debt Funds [Member] | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	26.00%	25.00%
Venture Private Equity Funds [Member] | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	31.00%	25.00%
Buyout Private Equity Funds [Member] | Private equity funds
Defined Benefit Plan Disclosure [Line Items]
Actual Allocation	43.00%	50.00%