Pension and Other Postretirement Benefits - Plan Assets (Details 4) - Pension Plans, Defined Benefit [Member] - USD ($) $ in Millions		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		$ 1,340.0	$ 1,739.6	$ 2,322.2
Equity Securities [Member]
Defined Benefit Plan, Target Allocation, Percentages of Assets [Abstract]
Target plan asset allocation percentage		60.00%
Fixed Income Securities [Member]
Defined Benefit Plan, Target Allocation, Percentages of Assets [Abstract]
Target plan asset allocation percentage		40.00%
Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		$ 1,340.0	1,739.6
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		39.1	35.4
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | U.S. Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		39.1	35.4
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Global Equity Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Other U.S. Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Global Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Fair Value, Recurring [Member] | Other Investment Companies [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		690.8	1,077.5
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | U.S. Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Global Equity Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		140.2	131.4
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		87.2	84.5
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Other U.S. Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		318.2	700.8
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Global Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		66.1	82.8
Fair Value, Inputs, Level 2 [Member] | Fair Value, Recurring [Member] | Other Investment Companies [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		79.1	78.0
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Recurring [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		729.9	1,112.9
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Recurring [Member] | U.S. Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		39.1	35.4
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Recurring [Member] | Global Equity Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		140.2	131.4
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Recurring [Member] | U.S. High-Yield Corporate Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		87.2	84.5
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Recurring [Member] | Other U.S. Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		318.2	700.8
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Recurring [Member] | Global Fixed Income Investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		66.1	82.8
Fair Value, Inputs, Level 1, 2 and 3 [Member] | Fair Value, Recurring [Member] | Other Investment Companies [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets		79.1	78.0
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | U.S. Equity Securities Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	[1]	367.2	355.8
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Global Equity Securities Common/Collective Trusts [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	[1]	196.9	178.2
Fair Value Measured at Net Asset Value Per Share [Member] | Fair Value, Recurring [Member] | Global Fixed Income Securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans [Line Items]
Fair value of plan assets	[2]	$ 46.0	$ 92.7

[1] Investments may include common stocks, options and futures.

[2] Investments may include investment-grade and high-yield corporate bonds, interest rate swaps, options and futures.