Basis of Presentation and Summary of Significant Accounting Policies (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended							9 Months Ended	12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2012
Change in accounting estimates
Operating expenses								$ (5,436)	$ (6,943)
Depreciation expense								(914)	(1,176)
Net income	241	212	178	218	179	199	165	543	849
Change in estimates of capitalized labor | Adjustments
Change in accounting estimates
Depreciation expense									52
Net income									32
Change in estimates of capitalized labor | Adjustments | Minimum
Change in accounting estimates
Labor capitalized as an asset									40
Operating expenses									40
Net income									25
Change in estimates of capitalized labor | Adjustments | Maximum
Change in accounting estimates
Labor capitalized as an asset									55
Operating expenses									55
Net income									$ 34