Accumulated Other Comprehensive Loss (Changes in Accumulated Other Comprehensive Loss by Component) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		$ (318)	$ (313)
Other comprehensive income before reclassifications		86	(14)
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit		(49)	(50)
Amortization– actuarial loss		40	59
Amortization– settlement loss		7	4
Other		(1)
Tax effect		1	(4)
Other comprehensive income (loss)		84	(5)	$ (109)
Ending balance		(234)	(318)	(313)
Pension Benefits
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit		(46)	(46)	(46)
Other Benefits
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit		(3)	(4)	(4)
Accumulated Defined Benefit Plans Adjustment | Pension Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(255)	(217)
Other comprehensive income before reclassifications		22	(44)
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	[1]	(46)	(46)
Amortization– actuarial loss	[1]	38	51
Amortization– settlement loss	[1]	7	4
Tax effect		1	(3)
Other comprehensive income (loss)		22	(38)
Ending balance		(233)	(255)	(217)
Accumulated Defined Benefit Plans Adjustment | Other Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		(70)	(104)
Other comprehensive income before reclassifications		64	31
Amounts reclassified from accumulated other comprehensive loss:
Amortization - prior service credit	[1]	(3)	(4)
Amortization– actuarial loss	[1]	2	8
Amortization– settlement loss	[1]	0	0
Tax effect		0	(1)
Other comprehensive income (loss)		63	34
Ending balance		(7)	(70)	(104)
Gain on Cash Flow Hedge
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		4	4
Other comprehensive income before reclassifications		0	0
Amounts reclassified from accumulated other comprehensive loss:
Tax effect		0	0
Other comprehensive income (loss)		0	0
Ending balance		4	4	4
Workers Compensation
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance		3	4
Other comprehensive income before reclassifications		0	(1)
Amounts reclassified from accumulated other comprehensive loss:
Other	[2]	(1)
Tax effect		0	0
Other comprehensive income (loss)		(1)	(1)
Ending balance		$ 2	$ 3	$ 4

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

[2] This amount was reclassified out of accumulated other comprehensive loss and is included in selling, general and administrative on the consolidated statements of income.