Retirement Plans and Other Postretirement Benefits - Narrative (Details)	9 Months Ended
	Sep. 30, 2019 USD ($)
Pension Benefits
Contributions
Voluntary employer contributions to pension plan	$ 150,000,000
Minimum employer contributions for the next three years	0
Maximum employer contributions for the next two years (up to)	350,000,000
Other Benefits
Contributions
Estimated future employer contributions in next three years	0
Retiree medical cost reimbursement	$ 30,000,000