Accumulated Other Comprehensive Loss (Changes in Accumulated Other Comprehensive Loss by Component) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ (231)	$ (234)
Other comprehensive income (loss) before reclassifications		49	(23)
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit		(36)	(42)
Amortization– actuarial loss		30	34
Amortization– settlement loss		53	52
Other		(6)	(2)
Tax effect		(3)	(16)
Other comprehensive income		87	3	$ 84
Ending balance		(144)	(231)	(234)
Pension Benefits
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit		(33)	(39)	(46)
Other Benefits
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit		(3)	(3)	(3)
Accumulated Defined Benefit Plans Adjustment | Pension Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(190)	(233)
Other comprehensive income (loss) before reclassifications		14	12
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	[1]	(33)	(39)
Amortization– actuarial loss	[1]	31	36
Amortization– settlement loss	[1]	53	52
Tax effect		(7)	(18)
Other comprehensive income		58	43
Ending balance		(132)	(190)	(233)
Accumulated Defined Benefit Plans Adjustment | Other Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(48)	(7)
Other comprehensive income (loss) before reclassifications		27	(38)
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	[1]	(3)	(3)
Amortization– actuarial loss	[1]	(1)	(2)
Amortization– settlement loss	[1]	0	0
Tax effect		2	2
Other comprehensive income		25	(41)
Ending balance		(23)	(48)	(7)
Gain on Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		4	4
Other comprehensive income (loss) before reclassifications		(1)	0
Amounts reclassified from accumulated other comprehensive loss:
Reclassified to earnings, net		(1)
Other comprehensive income		(2)	0
Ending balance		2	4	4
Workers Compensation
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		3	2
Other comprehensive income (loss) before reclassifications		9	3
Amounts reclassified from accumulated other comprehensive loss:
Other		(5)	(2)
Tax effect		2	0
Other comprehensive income		6	1
Ending balance		$ 9	$ 3	$ 2

[1] These accumulated other comprehensive loss components are included in the computation of net periodic benefit cost. See Note 22.