Summary of Significant Accounting Policies (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Jan. 01, 2019
New Accounting Pronouncements
Length of fiscal quarters, weeks	91 days
Operating lease liability	$ 1,384
Operating lease, right-of-use asset	$ 1,315
ASC Topic 842 - Leases
New Accounting Pronouncements
Operating lease liability		$ 1,400
Operating lease, right-of-use asset		$ 1,400