Benefit Plans Part 2 (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Stock Compensation Plan [Member]
Share-based compensation arrangement by share-based payment award, number of shares authorized	6
Share-based compensation arrangement by share-based payment award, number of shares available for grant	2.4
Allocated share-based compensation expense	$ 6	$ 5	$ 3
Employee service share-based compensation, tax benefit from compensation expense	2	2	1
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized	$ 10
Employee service share-based compensation, nonvested awards, total compensation cost not yet recognized, period for recognition	1.83
Share Awards [Member]
Share awards plan agreement	Share awards currently granted under the Plan include restricted shares, performance-based RSUs, and performance share units. Generally, restricted shares vest ratably over a four-year service period following the date of grant. Performance-based RSUs generally become payable within a range of 0% to 100% of the number of shares initially granted based upon the attainment of specific annual performance goals and vest ratably over a four-year service period following the date of grant. Performance share units become payable within a range of 0% to 200% of the number of shares initially granted based upon the attainment of specific performance goals achieved over a three year period.