Pension and Other Postretirement Employee Benefit Plans - Plan Assumptions (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Projected decrease in expense due to increased discount rates	$ 20
Interest crediting rate	4.90%
U.S. | Defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets	5.50%
U.S. | OPEB plans
Defined Benefit Plan Disclosure [Line Items]
Expected long-term rate of return on plan assets	4.30%