Leases and Capacity Purchase Agreements - Supplemental Cash Flow Information Related to Leases (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018		Dec. 31, 2017
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows for operating leases	$ 902	$ 1,078		$ 1,451
Operating cash flows for finance leases	70	53		24
Financing cash flows for finance leases	$ 151	$ 79	[1]	$ 84	[1]

[1] Amounts adjusted due to the adoption of Accounting Standards Update No. 2016-02, Leases (Topic 842). See Note 1 to the financial statements contained in Part II, Item 8 of this report for additional information.