Retirement Plans and Other Retiree Benefits - Summary of Amounts in AOCI (Details) $ in Millions	Dec. 31, 2018 USD ($)
Pension Plans
Estimated amounts that will be amortized from accumulated other comprehensive income [Abstract]
Net actuarial loss	$ 60
Net transition and prior service cost	0
Other Retiree Benefit Plans
Estimated amounts that will be amortized from accumulated other comprehensive income [Abstract]
Net actuarial loss	11
Net transition and prior service cost	$ 0