Leases - Lease Costs (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Finance lease cost:
Amortization of assets	$ 53	$ 53	$ 166	$ 146
Interest on lease liabilities	2	4	9	12
Operating Lease, Cost	70	170	220	381
Short-term lease cost	2	4	6	14
Variable lease cost	24	21	66	83
Sublease income	(3)	(1)	(4)	(2)
Total lease cost	$ 148	$ 251	$ 463	$ 634

Amount of interest expense on finance lease liability.

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-Name Accounting Standards Codification
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- Definition

Amount of amortization expense attributable to right-of-use asset from finance lease.

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- Definition

Amount of lease cost recognized by lessee for lease contract.

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Amount of single lease cost, calculated by allocation of remaining cost of lease over remaining lease term. Includes, but is not limited to, single lease cost, after impairment of right-of-use asset, calculated by amortization of remaining right-of-use asset and accretion of lease liability.

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-Publisher FASB
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Amount of short-term lease cost, excluding expense for lease with term of one month or less.

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- Definition

Amount of sublease income excluding finance and operating lease expense.

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- Definition

Amount of variable lease cost, excluded from lease liability, recognized when obligation for payment is incurred for finance and operating leases.

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