Leases Components of balance sheet (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Impairment of right-of-use assets associated with operating leases	$ 191	$ 139
Operating lease right-of-use assets (non-current)	786	931
Current portion of operating lease liabliities	251	208
Operating lease liabilities (non-current)	758	825
Other assets
Finance leases - Other assets (non-current)	113	123
Other current liabilities
Finance leases - Other current liabilities	24	19
Other liabilities
Finance leases - Other liabilities (non-current)	$ 118	$ 124