Background and Basis of Presentation Level 4 (Details) - Accounting Changes and Error Corrections (USD $) In Millions, unless otherwise specified	9 Months Ended				3 Months Ended	9 Months Ended				9 Months Ended	12 Months Ended	9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012	Dec. 31, 2011	Sep. 30, 2012 Accelerated depreciation [Member]	Sep. 30, 2012 Accelerated depreciation [Member]	Sep. 30, 2012 Income tax benefit error correction [Member]	Sep. 30, 2012 As Previously Reported [Member]	Dec. 31, 2011 As Previously Reported [Member]	Sep. 30, 2012 Cash and Cash Equivalents [Member]	Dec. 31, 2011 Cash and Cash Equivalents [Member]	Sep. 30, 2012 Net cash provided by operating activities [Member]
Prior Period Reclassification Adjustment					$ 1	$ 7	$ 22			$ (18)	$ (12)	$ (6)
Net Cash Provided by (Used in) Operating Activities	(23)	21						27
Cash	$ 332	$ 319	$ 401	$ 416				$ 337	$ 428