Income Taxes - Deferred Taxes (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 1,301	$ 1,495
Capital loss carryforward	480	483
Pension, postretirement and other benefits	2,089	2,956
Investments	314	0
Deferred revenue	2,288	1,929
Lease liabilities	2,452	2,185
Other	494	479
Valuation allowance	(833)	(460)	$ (58)
Total deferred tax assets	8,585	9,067
Deferred tax liabilities:
Depreciation	4,463	4,507
Operating lease assets	1,676	1,324
Intangible assets	1,097	1,076
Other	55	172
Total deferred tax liabilities	7,291	7,079
Net deferred tax assets	$ 1,294	$ 1,988