Accounting Pronouncements - Leases (Details) - USD ($) $ in Millions	Jan. 01, 2019	Mar. 31, 2019	Dec. 31, 2018
Lessee Disclosure [Abstract]
Practical expedient package adopted	true
Assets [Abstract]
Other current assets	$ 139	$ 184	$ 140
Operating lease right-of-use assets	$ 244	$ 236
Operating Lease, Right-of-Use Asset, Statement of Financial Position [Extensible List]	us-gaap:OtherAssetsMember	us-gaap:OtherAssetsMember
Other assets	$ 1,384
Liabilities [Abstract]
Other current liabilities	489	$ 500	492
Current operating lease liabilities	$ 53	$ 54
Operating Lease, Liability, Current, Statement of Financial Position [Extensible List]	us-gaap:OtherCurrentLiabilitiesMember	us-gaap:OtherCurrentLiabilitiesMember
Other liabilities	$ 273	$ 416	287
Noncurrent operating lease liabilities	$ 182	$ 181
Operating Lease, Liability, Noncurrent, Statement of Financial Position [Extensible List]	us-gaap:OtherNoncurrentLiabilitiesMember	us-gaap:OtherLiabilitiesMember
Effect of Tax Cuts and Jobs Act of 2017 [Abstract]
Reclassification of stranded tax effects	$ 79
As Previously reported
Assets [Abstract]
Other current assets			140
Other assets			1,409
Liabilities [Abstract]
Other current liabilities			492
Other liabilities			$ 287
ASU 2016-02 | Adjustments Due to Adoption
Assets [Abstract]
Other current assets	(1)
Operating lease right-of-use assets	244
Other assets	(25)
Liabilities [Abstract]
Other current liabilities	(3)
Current operating lease liabilities	53
Other liabilities	(14)
Noncurrent operating lease liabilities	$ 182