Other Comprehensive Income (Loss) - Changes in AOCI Balance by Component (Details) - USD ($) $ in Millions	3 Months Ended								6 Months Ended
	Jun. 30, 2021		Mar. 31, 2021		Jun. 30, 2020		Mar. 31, 2020		Jun. 30, 2021
Other Comprehensive Income (Loss)
Income Before Reclassifications									$ 28
Amounts Reclassified to Net Earnings									33
Tax Expense									(14)
Total Other Comprehensive Income	$ (21)		$ 68		$ 20		$ 3		47
Pension and Other Post-Employment Benefits
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2020, Net of Tax			(598)						(598)
Other Comprehensive Income (Loss)
Income Before Reclassifications									0
Amounts Reclassified to Net Earnings									33
Tax Expense									(7)
Total Other Comprehensive Income									26
Balance June 30, 2021, Net of Tax	(572)								(572)
Interest Rate Derivatives
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2020, Net of Tax			62						62
Other Comprehensive Income (Loss)
Income Before Reclassifications									28
Amounts Reclassified to Net Earnings									0
Tax Expense									(7)
Total Other Comprehensive Income									21
Balance June 30, 2021, Net of Tax	83								83
Other
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2020, Net of Tax			(62)						(62)
Other Comprehensive Income (Loss)
Income Before Reclassifications									0
Amounts Reclassified to Net Earnings									0
Tax Expense									0
Total Other Comprehensive Income									0
Balance June 30, 2021, Net of Tax	(62)								(62)
Accumulated Other Comprehensive Income (Loss)
AOCI Attributable to Parent, Net of Tax [Roll Forward]
Balance December 31, 2020, Net of Tax			(598)						(598)
Other Comprehensive Income (Loss)
Total Other Comprehensive Income	(21)	[1]	$ 68	[1]	$ 20	[2]	$ 3	[2]
Balance June 30, 2021, Net of Tax	$ (551)								$ (551)

[1] Accumulated Other Comprehensive Loss balances shown above are net of tax. The associated taxes were $137 million and $142 million as of first and second quarters 2021, respectively. For additional information, see Note 11, Other Comprehensive Income.

[2] Accumulated Other Comprehensive Loss balances shown above are net of tax. The associated taxes were $183 million and $178 million as of first and second quarters 2020, respectively. For additional information, see Note 11, Other Comprehensive Income.