Pension and Other Postemployment Benefits (Details 5) - OPEB - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 438	$ 473
Asset Allocation	100.00%	100.00%
Cash and short-term securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 25	$ 41
Asset Allocation	6.00%	9.00%
Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 219	$ 230
Asset Allocation	50.00%	48.00%
International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 4	$ 6
Asset Allocation	1.00%	1.00%
U.S. treasuries
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 42	$ 41
Asset Allocation	10.00%	9.00%
Government bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 114	$ 110
Asset Allocation	26.00%	23.00%
Corporate bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 27	$ 32
Asset Allocation	6.00%	7.00%
High yield debt
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 1	$ 2
Asset Allocation	0.00%	0.00%
Mortgaged-backed securities (non-government)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 3	$ 3
Asset Allocation	1.00%	1.00%
Hedge funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 1	$ 5
Asset Allocation	0.00%	1.00%
Real estate funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 2	$ 3
Asset Allocation	0.00%	1.00%
Level 1
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 220	$ 233
Level 1 | Cash and short-term securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	219	230
Level 1 | International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	1	3
Level 1 | U.S. treasuries
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | Government bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | Corporate bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | High yield debt
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | Mortgaged-backed securities (non-government)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | Hedge funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 1 | Real estate funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 2
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	216	237
Level 2 | Cash and short-term securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	25	41
Level 2 | Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 2 | International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	3	3
Level 2 | U.S. treasuries
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	42	41
Level 2 | Government bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	114	110
Level 2 | Corporate bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	27	32
Level 2 | High yield debt
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	1	2
Level 2 | Mortgaged-backed securities (non-government)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	3	3
Level 2 | Hedge funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	1	5
Level 2 | Real estate funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	2	3
Level 3 | Cash and short-term securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Domestic
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | International
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | U.S. treasuries
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Government bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Corporate bonds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | High yield debt
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Mortgaged-backed securities (non-government)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Hedge funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	0	0
Level 3 | Real estate funds
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Pension investments measured at fair value	$ 2	$ 3	$ 5