Shareholders' Equity Schedule of Net Income from Participating Securities (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income from participating securities	$ 2	$ 3	$ 5	$ 6
Continuing Operations [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income from participating securities	2	3	5	6
Discontinued Operations [Member]
Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items]
Net income from participating securities	$ 0	$ 0	$ 0	$ 0