Fair Value Measurements (Fair Value Hierarchy Classification) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Short-term borrowings	$ 1,066	$ 392
Portion at Other than Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term receivables	137	127
Customer financing notes receivable	612	609
Short-term borrowings	1,066	392
Long-term debt (excluding capitalized leases)	26,256	27,067
Long-term liabilities	310	362
Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term receivables	130	121
Customer financing notes receivable	594	596
Short-term borrowings	1,066	392
Long-term debt (excluding capitalized leases)	27,153	29,180
Long-term liabilities	276	330
Fair Value Level 1 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term receivables	0	0
Customer financing notes receivable	0	0
Short-term borrowings	0	0
Long-term debt (excluding capitalized leases)	0	0
Long-term liabilities	0
Fair Value Level 2 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term receivables	130	121
Customer financing notes receivable	594	596
Short-term borrowings	930	300
Long-term debt (excluding capitalized leases)	26,925	28,970
Long-term liabilities	276	330
Fair Value Level 3 [Member] | Estimate of Fair Value, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-term receivables	0	0
Customer financing notes receivable	0	0
Short-term borrowings	136	92
Long-term debt (excluding capitalized leases)	228	210
Long-term liabilities	0	0
Fair Value, Measurements, Recurring [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	49	64
Derivative Assets	341	253
Fair Value, Measurements, Recurring [Member] | Fair Value Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	49	64
Derivative Assets	0	0
Derivative Liabilities	0	0
Fair Value, Measurements, Recurring [Member] | Fair Value Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Derivative Assets	341	253
Derivative Liabilities	72	78
Fair Value, Measurements, Recurring [Member] | Fair Value Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Available-for-sale securities	0	0
Derivative Assets	0	0
Derivative Liabilities	$ 0	$ 0