Pension and Postretirement Plans - Narratives (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018
Other Postretirement Benefit Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Postretirement health plans, contributions	$ 9.0
Contributions to pension plans	3.4	$ 3.5
Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Contributions to pension plans	2.5	$ 2.8
Qualified Plan [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Postretirement health plans, contributions	3.0
Nonqualified Plan [Member] | Pension Plans, Defined Benefit [Member]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Postretirement health plans, contributions	$ 3.0