Pension and Other Post-Employment Benefits (Details) - USD ($) $ in Millions		3 Months Ended
	Mar. 11, 2021	Mar. 31, 2021	Mar. 31, 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	$ 5
Mark-to-market adjustment			423
Pension
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service costs		49	52
Interest costs		56	75
Expected return on plan assets		(163)	(153)
Amortization of prior service costs (credits)		1	10
One-time termination benefit		0	8
Pension and OPEB mark-to-market adjustment		0	386
Net periodic costs (credits), including amounts capitalized		(57)	378
Net periodic costs (credits), recognized in earnings		(78)	358
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
Interest costs		3	4
Expected return on plan assets		(10)	(8)
Amortization of prior service costs (credits)		(4)	(33)
One-time termination benefit		0	0
Pension and OPEB mark-to-market adjustment		0	37
Net periodic costs (credits), including amounts capitalized		(10)	1
Net periodic costs (credits), recognized in earnings		$ (10)	$ 1