Comprehensive Income (Loss) (Reclassification Out of AOCI) (Details) - Reclassification out of Accumulated Other Comprehensive Income [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Pension Benefits [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI, before tax	[1],[2]	$ (11)	$ (7)
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	3
Amounts reclassified from AOCI, net of tax	[1],[2]	(7)	(4)
Postretirement Costs [Member] | Accumulated Defined Benefit Plans Adjustment, Net Prior Service Cost (Credit) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI, before tax	[1],[2]	2	1
Postretirement Costs [Member] | Accumulated Defined Benefit Plans Adjustment, Net Unamortized Gain (Loss) [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Amounts reclassified from AOCI, before tax	[1],[2]		(3)
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	(2)
Amounts reclassified from AOCI, tax	[1],[2]	(1)	1
Amounts reclassified from AOCI, net of tax	[1],[2]	$ 1	$ (1)

[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).