Schedule of Valuation and Qualifying Accounts (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	$ 2,420	$ 2,731	$ 2,474
Charged to costs and expenses	536	(110)	411
Deductions	259	201	154
Balance at end of period	2,697	2,420	2,731
Credit losses [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	405	435	570
Charged to costs and expenses	199	152	2
Deductions	220	182	137
Balance at end of period	384	405	435
Doubtful receivables [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	120	106	110
Charged to costs and expenses	374	33	13
Deductions	39	19	17
Balance at end of period	455	120	106
Inventories (primarily service part obsolescence) [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	262	267	249
Charged to costs and expenses	(8)	(5)	18
Deductions	0	0	0
Balance at end of period	254	262	267
Deferred tax assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at beginning of period	1,633	1,923	1,545
Charged to costs and expenses	(29)	(290)	378
Deductions	0	0	0
Balance at end of period	1,604	1,633	1,923
Valuation Allowance Of Deferred Tax Assets Recognized In Accumulated Other Comprehensive Income Loss [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Charged to costs and expenses	(428)	(243)	264
Valuation Allowance of Deferred Tax Assets Recognized in Income Statement [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Charged to costs and expenses	$ 399	$ (47)	$ 114