Savings, Pension and Other Postretirement Employee Benefit Plans - Investments at Fair Value for Company Sponsored Pension Benefit Plans Within Fair Value Hierarchy (Details) - USD ($)	Dec. 31, 2019	Dec. 31, 2017
Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,000,000	$ 2,000,000
defined benefit plan net asset value	0	0
Common and collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	304,600,000	266,800,000
defined benefit plan net asset value	304,600,000	266,800,000
Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	306,600,000	268,800,000
defined benefit plan net asset value	304,600,000	266,800,000
Fair Value, Inputs, Level 1 | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2,000,000	2,000,000
Fair Value, Inputs, Level 1 | Common and collective trusts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Fair Value, Inputs, Level 1 | Investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 2,000,000	$ 2,000,000