Accounting Changes - Tax Reform and Leases (Details) - USD ($) $ in Millions		9 Months Ended
	Jan. 01, 2018	Sep. 30, 2019		Jan. 01, 2019
Leases
Package of practical expedients		true
Operating right-of-use assets		$ 4,901	[1]	$ 4,800
Financing right-of-use assets				200
Operating lease liabilities		5,167		5,100
Financing lease liabilities		$ 155		$ 200
Stranded tax effects
Reclassification from AOCI to retained earnings for stranded tax effects of U.S. tax reform	$ (2,400)

[1] * Reflects the adoption of the FASB guidance on leases. Refer to note 2, “Accounting Changes” and note 5, “Leases.”