Basis of Presentation (Details 2) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended				12 Months Ended		3 Months Ended	12 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2012 Change in estimates of capitalized labor Minimum	Mar. 31, 2012 Change in estimates of capitalized labor Maximum	Dec. 31, 2012 Change in estimates of capitalized labor Expected Minimum	Dec. 31, 2012 Change in estimates of capitalized labor Expected Maximum	Mar. 31, 2012 Change in estimates of economic lives and net salvage value	Dec. 31, 2012 Change in estimates of economic lives and net salvage value Expected
Change in accounting estimates
Depreciation expense							$ 10	$ 40
Labor capitalized as an asset			15	20
Operating expense	3,956	1,232	(15)	(20)	(60)	(80)
Net income	$ 200	$ 211	$ 9	$ 12	$ 36	$ 48	$ (6)	$ (24)
Basic earnings per common share	$ 0.32	$ 0.69	$ 0.01	$ 0.02	$ 0.06	$ 0.08	$ (0.01)	$ (0.04)
Diluted earnings per common share	$ 0.32	$ 0.69	$ 0.01	$ 0.02	$ 0.06	$ 0.08	$ (0.01)	$ (0.04)