Pension and Other Postretirement Benefit Plans - Recurring Fair Value Measures (Details) - USD ($) $ in Millions	Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Pension [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	$ 521.3		$ 544.2		$ 501.6
Pension [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	144.1		120.4
Pension [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	305.0		351.6
Pension [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	72.2		72.2
Pension [Member] | U.S. Large-cap [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	76.0	[1]	88.5	[2]
Pension [Member] | U.S. Large-cap [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	33.9	[1]	32.1	[2]
Pension [Member] | U.S. Large-cap [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	42.1	[1]	56.4	[2]
Pension [Member] | U.S. Large-cap [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	[1]	0.0	[2]
Pension [Member] | U.S. Mid-cap Growth [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	31.9	[1]	37.5	[2]
Pension [Member] | U.S. Mid-cap Growth [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	14.2	[1]	13.6	[2]
Pension [Member] | U.S. Mid-cap Growth [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	17.7	[1]	23.9	[2]
Pension [Member] | U.S. Mid-cap Growth [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	[1]	0.0	[2]
Pension [Member] | U.S. Small-cap [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	32.4	[1]	38.3	[2]
Pension [Member] | U.S. Small-cap [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	14.5	[1]	13.9	[2]
Pension [Member] | U.S. Small-cap [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	17.9	[1]	24.4	[2]
Pension [Member] | U.S. Small-cap [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	[1]	0.0	[2]
Pension [Member] | Mutual Funds [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	8.4
Pension [Member] | Mutual Funds [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	8.4
Pension [Member] | Mutual Funds [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0
Pension [Member] | Mutual Funds [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0
Pension [Member] | International [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	86.7		92.0
Pension [Member] | International [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	44.7		46.1
Pension [Member] | International [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	42.0		45.9
Pension [Member] | International [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Debt Securities - Mutual Funds [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.1		0.1
Pension [Member] | Debt Securities - Mutual Funds [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.1		0.1
Pension [Member] | Debt Securities - Mutual Funds [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Debt Securities - Mutual Funds [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Debt Securities - Fixed Income [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	188.0		203.7
Pension [Member] | Debt Securities - Fixed Income [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	2.7		2.7
Pension [Member] | Debt Securities - Fixed Income [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	185.3		201.0
Pension [Member] | Debt Securities - Fixed Income [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Cash and Cash Equivalents [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	25.6		11.9
Pension [Member] | Cash and Cash Equivalents [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	25.6		11.9
Pension [Member] | Cash and Cash Equivalents [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Cash and Cash Equivalents [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Private Equity Funds [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	43.3		43.3
Pension [Member] | Private Equity Funds [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Private Equity Funds [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Private Equity Funds [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	43.3		43.3
Pension [Member] | Real Estate [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	28.9		28.9
Pension [Member] | Real Estate [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Real Estate [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Pension [Member] | Real Estate [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	28.9		28.9
Postretirement Health and Life [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	153.4		163.2		$ 157.0
Postretirement Health and Life [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	133.0		140.4
Postretirement Health and Life [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	8.4		9.9
Postretirement Health and Life [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	12.0		12.9
Postretirement Health and Life [Member] | U.S. Large-cap [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	28.2	[3]	29.3	[4]
Postretirement Health and Life [Member] | U.S. Large-cap [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	28.2	[3]	29.3	[4]
Postretirement Health and Life [Member] | U.S. Large-cap [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	[3]	0.0	[4]
Postretirement Health and Life [Member] | U.S. Large-cap [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	[3]	0.0	[4]
Postretirement Health and Life [Member] | U.S. Mid-cap Growth [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	19.1	[3]	20.0	[4]
Postretirement Health and Life [Member] | U.S. Mid-cap Growth [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	19.1	[3]	20.0	[4]
Postretirement Health and Life [Member] | U.S. Mid-cap Growth [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	[3]	0.0	[4]
Postretirement Health and Life [Member] | U.S. Mid-cap Growth [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	[3]	0.0	[4]
Postretirement Health and Life [Member] | U.S. Small-cap [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	12.1	[3]	12.6	[4]
Postretirement Health and Life [Member] | U.S. Small-cap [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	12.1	[3]	12.6	[4]
Postretirement Health and Life [Member] | U.S. Small-cap [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	[3]	0.0	[4]
Postretirement Health and Life [Member] | U.S. Small-cap [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0	[3]	0.0	[4]
Postretirement Health and Life [Member] | International [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	26.8		30.6
Postretirement Health and Life [Member] | International [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	26.8		30.6
Postretirement Health and Life [Member] | International [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | International [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | Debt Securities - Mutual Funds [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	45.2		44.5
Postretirement Health and Life [Member] | Debt Securities - Mutual Funds [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	45.2		44.5
Postretirement Health and Life [Member] | Debt Securities - Mutual Funds [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | Debt Securities - Mutual Funds [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | Debt Securities - Fixed Income [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	8.4		9.9
Postretirement Health and Life [Member] | Debt Securities - Fixed Income [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | Debt Securities - Fixed Income [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	8.4		9.9
Postretirement Health and Life [Member] | Debt Securities - Fixed Income [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | Cash and Cash Equivalents [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	1.6		3.4
Postretirement Health and Life [Member] | Cash and Cash Equivalents [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	1.6		3.4
Postretirement Health and Life [Member] | Cash and Cash Equivalents [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | Cash and Cash Equivalents [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | Private Equity Funds [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	12.0		12.9
Postretirement Health and Life [Member] | Private Equity Funds [Member] | Level 1 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | Private Equity Funds [Member] | Level 2 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	0.0		0.0
Postretirement Health and Life [Member] | Private Equity Funds [Member] | Level 3 [Member]
Recurring Fair Value Measures [Line Items]
Fair Value of Assets	$ 12.0		$ 12.9

[1] The underlying investments classified under U.S. Equity Securities consist of money market funds (Level 1) and actively-managed funds (Level 2), which are combined with futures, and settle daily, to achieve the returns of the U.S. Equity Securities Large-cap, Mid-cap Growth, and Small-cap funds. Our exposure with respect to these investments includes both the futures and the underlying investments.

[2] The underlying investments classified under U.S. Equity Securities consist of money market funds (Level 1) and actively-managed funds (Level 2), which are combined with futures, and settle daily, to achieve the returns of the U.S. Equity Securities Large-cap, Mid-cap Growth, and Small-cap funds. Our exposure with respect to these investments includes both the futures and the underlying investments.

[3] The underlying investments classified under U.S. Equity Securities consist of mutual funds (Level 1).

[4] The underlying investments classified under U.S. Equity Securities consist of mutual funds (Level 1).