Leases Leases - Balance Sheet Classification (Details) $ in Millions	Mar. 31, 2019 USD ($)	[1]
Leases [Abstract]
Operating Lease, Right-of-Use Asset	$ 456
Operating Lease, Liability, Current	27
Operating Lease, Liability, Noncurrent	$ 488

[1] (1) As noted above, we have elected the short-term lease measurement and recognition exemption and do not establish ROU assets or liabilities for operating leases with terms of 12 months or less.