Leases (Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Leases [Abstract]
Cash payments for operating leases	$ 2,004	$ 1,661
New operating lease assets obtained in exchange for operating lease liabilities	$ 2,765	$ 4,391