Income Taxes - Completion of IRS Tax Examinations (Details) (Internal Revenue Service (IRS) [Member], USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Sep. 30, 2013 Tax Years 2009 And 2010 [Member]	Dec. 31, 2011 Tax Years 2007 And 2008 [Member]
Income Tax Examination [Line Items]
Increase (decrease) to shareholders' net income resulting from IRS examination	$ 18	$ 24