Segment Information (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment income	$ 483	$ 619	$ 655	$ 653	$ 641	$ (685)	$ 715	$ 782	$ 2,410	$ 1,453	$ 2,713
Other operating revenues	4,438	4,514	4,541	4,538	4,542	4,515	4,525	4,513	18,031	18,095	18,376
Depreciation and amortization									(4,428)	(4,541)	(4,780)
Impairment of goodwill		1,100							0	1,092	0
Other unassigned operating expenses									(3,347)	(3,502)	(3,244)
Income tax expense									(338)	(463)	(473)
Other expenses, net									(1,300)	(1,229)	(1,463)
Net income (loss)	188	188	193	203	239	(1,045)	269	298	772	(239)	777
Operating segments (segments)
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Total segment income									8,519	8,928	9,173
Unallocated amount to segment
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Other operating revenues									1,003	1,000	1,056
Depreciation and amortization									(4,428)	(4,541)	(4,780)
Impairment of goodwill									0	1,092	0
Other unassigned operating expenses									(2,684)	(2,842)	(2,736)
Income tax expense									(338)	(463)	(473)
Other expenses, net									$ (1,300)	$ (1,229)	$ (1,463)