Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Deferred income tax assets:
Lease and rents	$ 267	$ 277
Inventory	23	28
Employee benefits	191	243
Bad debts and other allowances	294	243
Retirement benefits	47	130
Net operating loss and capital loss carryforwards	480	529
Deferred income	36	104
Insurance reserves	430	467
Investments	0	11
Other	451	242
Valuation allowance	(374)	(520)
Total deferred income tax assets	1,845	1,754
Deferred income tax liabilities:
Investments	(289)	0
Depreciation and amortization	(8,850)	(9,431)
Total deferred income tax liabilities	(9,139)	(9,431)
Net deferred income tax liabilities	$ (7,294)	$ (7,677)