Management Compensation Plans (Schedule of Time-vested Cash Awards Activity) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense	$ 4	$ 7	$ 7
Active Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments	6	5	6
Terminated Employee [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Payments	$ 0	$ 1	$ 1