Compensation and Benefit Plans (Supplemental Stock-Based Compensation) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (benefit)	$ 7	[1]	$ 7	[1]	$ 9	[1]
Income tax benefits related to stock compensation expense	3		3		4
Excess tax benefits	5	[2]	2	[2]	1	[2]
Weighted average grant date fair value per option granted (in dollars per share)	$ 5.22		$ 5.61		$ 4.92
Fair value of options vested	3		3		3
Cash used to purchase shares to settle options	44		18		11
Cash from participants to exercise stock options	26		12		6
Value of options exercised	18		6		4
Tax benefit from options exercised	6		2		2
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (benefit)	3	[1]	2	[1]	4	[1]
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (benefit)	1	[1]	1	[1]	2	[1]
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (benefit)	1	[1]	2	[1]	1	[1]
Weighted average grant date fair value per share granted	$ 43.16		$ 38.03		$ 33.30
Value of shares settled	1		2		0
Tax benefits realized from settlements of awards	0		1		0
Other Stock Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense (benefit)	2	[1]	2	[1]	2	[1]
Performance shares classified as equity awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value per share granted	$ 51.41	[3]	$ 31.14	[3]	$ 32.50	[3]
Fair value of shares vested	$ 1.4	[3]	$ 0.8	[3]	$ 0.9	[3]

[1] Reflected in administration and general on the consolidated statements of operations.

[2] Reflected in excess tax benefits related to stock-based awards in cash flows from financing activities on the consolidated statements of cash flows.

[3] There were no settlements of awards for performance shares in 2012, 2011 and 2010 as performance targets were not met.