Impairments - Fair Value Measurements, Nonrecurring (Details) - Nonrecurring - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets Held-for-sale, Long Lived, Fair Value Disclosure	$ 0		$ 0
Long-lived assets, Fair Value	56	$ 108	56	$ 108	$ 39
Long-lived assets, Impairment	$ 0	$ 8	$ 24	$ 50