Income Taxes, Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current:
Country	$ (1,067)	$ 331	$ 573
U.S. state / Canadian provincial	6	137	103
Total current	(1,061)	468	676
Deferred:
Country	179	262	170
U.S. state / Canadian provincial	(21)	(28)	33
Total deferred	158	234	203
Income tax expense (benefit)	(903)	702	879
U.S. [Member]
Current:
Country	(1,033)	145	432
U.S. state / Canadian provincial	9	37	37
Total current	(1,024)	182	469
Deferred:
Country	126	290	145
U.S. state / Canadian provincial	(51)	(16)	19
Total deferred	75	274	164
Income tax expense (benefit)	(949)	456	633
International [Member]
Current:
Country	(34)	186	141
U.S. state / Canadian provincial	(3)	100	66
Total current	(37)	286	207
Deferred:
Country	53	(28)	25
U.S. state / Canadian provincial	30	(12)	14
Total deferred	83	(40)	39
Income tax expense (benefit)	$ 46	$ 246	$ 246