Retirement Benefits and Trusteed Assets - VEBA Contributions (Details) - USD ($) $ / shares in Units, $ in Millions		9 Months Ended
	Mar. 07, 2018	Sep. 30, 2018
Defined Contribution Plan Disclosure [Line Items]
Amount		$ 175
Pension Benefits
Defined Contribution Plan Disclosure [Line Items]
Number of Shares (in shares)	1,751,401
Price per Share (in dollars per share)	$ 99.92
Amount	$ 175