Retirement Plans and Other Postretirement Benefits - Narrative (Details) - USD ($) $ in Millions		9 Months Ended
	Jan. 04, 2021	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial pre-65 ultimate health care cost trend rate (as a percent)			2.00%	4.75%
Transfer to active union medical account	$ 106
Other Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Transfer to active union medical account	106
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Transfer to active union medical account	$ 106
Contributions
Voluntary contributions		$ 100
Minimum employer contributions for the next three years		$ 0