Retirement Plans and Other Postretirement Benefits - Narrative (Details) - USD ($)		3 Months Ended
	Jan. 04, 2021	Mar. 31, 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)				4.75%
Initial post-65 healthcare cost trend rate (as a percent)			2.00%
Transfer to active union medical account	$ (106,000,000)
Contributions
Expected voluntary employer contributions in the next fiscal year		$ 0
Expected voluntary employer contributions in the year after next fiscal year		0
Other Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Transfer to active union medical account	106,000,000
Contributions
Estimated future employer contributions in next three years		0
Pension Benefits
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Transfer to active union medical account	$ (106,000,000)
Contributions
Voluntary contributions		0
Minimum employer contributions for the next three years		0
Expected voluntary employer contributions in the remainder of the current fiscal year		$ 100,000,000