Accumulated Other Comprehensive Loss (Changes in Accumulated Other Comprehensive Loss by Component) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ (144)	$ (231)
Other comprehensive income (loss) before reclassifications, net of tax of ($52)		(162)	49
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit		(45)	(36)
Amortization– actuarial loss		21	30
Amortization– settlement loss		9	53
Other		(5)	(5)
Tax effect		6	(4)
Other comprehensive income (loss)		(176)	87	$ 3
Ending balance		(320)	(144)	(231)
Other comprehensive income (loss) before reclassifications, tax		(52)	23
Pension Benefits
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit		(45)	(33)	(39)
Other Benefits
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit		0	(3)	(3)
Accumulated Defined Benefit Plans Adjustment | Pension Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(132)	(190)
Other comprehensive income (loss) before reclassifications, net of tax of ($52)		(71)	14
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	[1]	(45)	(33)
Amortization– actuarial loss	[1]	22	31
Amortization– settlement loss	[1]	9	53
Tax effect		5	(7)
Other comprehensive income (loss)		(80)	58
Ending balance		(212)	(132)	(190)
Accumulated Defined Benefit Plans Adjustment | Other Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(23)	(48)
Other comprehensive income (loss) before reclassifications, net of tax of ($52)		(92)	27
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	[1]	0	(3)
Amortization– actuarial loss	[1]	(1)	(1)
Amortization– settlement loss	[1]	0	0
Tax effect		0	2
Other comprehensive income (loss)		(93)	25
Ending balance		(116)	(23)	(48)
Gain on Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		2	4
Other comprehensive income (loss) before reclassifications, net of tax of ($52)		0	(1)
Amounts reclassified from accumulated other comprehensive loss:
Reclassified to earnings, net		(1)
Tax effect		0	(1)
Other comprehensive income (loss)		(1)	(2)
Ending balance		1	2	4
Workers Compensation
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		9	3
Other comprehensive income (loss) before reclassifications, net of tax of ($52)		1	9
Amounts reclassified from accumulated other comprehensive loss:
Other		(4)	(5)
Tax effect		1	2
Other comprehensive income (loss)		(2)	6
Ending balance		$ 7	$ 9	$ 3

[1] These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 23.