Other Comprehensive Income / (Loss) - Changes in AOCI Balance by Components (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Other Comprehensive Income (Loss):
Effects				$ (107)
(Loss) Income Before Reclassifications		$ 53	$ (48)	(119)
Amounts Reclassified to Net Earnings		52	31	32
Tax Benefit (Expense)		(28)	3	19
Total Other Comprehensive Income (Loss) (Note 16)		77	(14)	(175)
Pension and Other Post-Employment Benefits
Other Comprehensive Income (Loss):
Beginning Balance		(619)	(604)	(440)
Effects				(108)
(Loss) Income Before Reclassifications		(17)	(43)	(111)
Amounts Reclassified to Net Earnings		47	23	38
Tax Benefit (Expense)		(9)	5	17
Total Other Comprehensive Income (Loss) (Note 16)		21	(15)	(164)
Ending Balance		(598)	(619)	(604)
Interest Rate Derivatives
Other Comprehensive Income (Loss):
Beginning Balance		0	0	0
Effects				0
(Loss) Income Before Reclassifications		80	0	0
Amounts Reclassified to Net Earnings		0	0	0
Tax Benefit (Expense)		(18)	0	0
Total Other Comprehensive Income (Loss) (Note 16)		62	0	0
Ending Balance		62	0	0
Other
Other Comprehensive Income (Loss):
Beginning Balance		(56)	(57)	(46)
Effects				1
(Loss) Income Before Reclassifications		(10)	(5)	(8)
Amounts Reclassified to Net Earnings		5	8	(6)
Tax Benefit (Expense)		(1)	(2)	2
Total Other Comprehensive Income (Loss) (Note 16)		(6)	1	(11)
Ending Balance		(62)	(56)	(57)
Accumulated Other Comprehensive Income (Loss)
Other Comprehensive Income (Loss):
Beginning Balance		(675)	(661)	(486)
Total Other Comprehensive Income (Loss) (Note 16)	[1]	77	(14)	(175)
Ending Balance		$ (598)	$ (675)	$ (661)

[1] Accumulated Other Comprehensive Loss year-end balances shown above are net of tax. The associated taxes were $156 million, $184 million and $180 million for 2020, 2019 and 2018, respectively. For additional information see Note 16, Other Comprehensive Income.