Leases Supplemental Lease Disclosures (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Leases [Abstract]
Operating cash outflows from operating leases	$ 28	$ 32
Operating cash outflows from finance leases	1	1
Financing cash outflows from finance leases	2	2
ROU assets obtained in exchange of new operating lease liabilities	19	19
ROU assets obtained in exchange of new finance lease liabilities		0	$ 2
Loss on sale leaseback transactions (short-term)	$ 0	$ 36
Operating lease, weighted average remaining lease term	7 years 8 months 12 days	6 years 8 months 12 days
Finance lease, weighted average remaining lease term	6 years 4 months 24 days	7 years 10 months 24 days
Operating lease, weighted average discount rate	9.20%	13.10%
Finance lease, weighted average discount rate	9.10%	5.60%