Pension and Other Post-Employment Benefits (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
	Mar. 11, 2021	Sep. 30, 2021	Sep. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension and OPEB prior service costs amortized out of AOCI		$ 1	$ 1		$ 3	$ 7
Mark-to-market adjustment				$ 423
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs		48	47		145	147
Interest costs		57	71		170	216
Expected return on plan assets		(163)	(156)		(489)	(464)
Amortization of prior service costs (credits)		1	1		3	12
One-time termination benefit					0	8
Pension and OPEB mark-to-market adjustment					0	386
Net periodic credits, including amounts capitalized		(57)	(37)		(171)	305
Net periodic credits, recognized in earnings		(80)	(56)		(243)	240
Net accelerated credits				$ 18
Estimated return	7.50%
OPEB
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs		1	1		3	3
Interest costs		3	4		8	12
Expected return on plan assets		(10)	(9)		(27)	(25)
Amortization of prior service costs (credits)		(4)	(4)		(13)	(42)
One-time termination benefit					0	0
Pension and OPEB mark-to-market adjustment					0	37
Net periodic credits, including amounts capitalized		(10)	(8)		(29)	(15)
Net periodic credits, recognized in earnings		$ (10)	$ (8)		$ (30)	$ (15)