Comprehensive Income (Loss) (Reclassification Out of AOCI) (Details) - Reclassification out of Accumulated Other Comprehensive Income [Member] - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits [Member] | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI, before tax	[1],[2]	$ (10)	$ (6)	$ (21)	$ (13)
Pension Benefits [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI, tax	[1],[2]	4	2	8	5
Amounts reclassified from AOCI, net of tax	[1],[2]	(6)	(4)	(13)	(8)
Postretirement Costs [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI, before tax	[1],[2]	3	1	5	2
Postretirement Costs [Member] | Accumulated Defined Benefit Plans Adjustment, Net Gain (Loss) Attributable to Parent [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI, before tax	[1],[2]	(1)	(2)	(1)	(5)
Postretirement Costs [Member] | Amortization Of Defined Benefit Cost Items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI, before tax	[1],[2]	2	(1)	4	(3)
Amounts reclassified from AOCI, tax	[1],[2]	(1)		(2)	1
Amounts reclassified from AOCI, net of tax	[1],[2]	$ 1	$ (1)	$ 2	$ (2)

[1] Amounts in parentheses indicate losses.

[2] These accumulated other comprehensive loss components are included in the computation of net periodic pension and OPEB costs (see Note 13 - Retirement Plans for additional details).