Fair Value Measurements (Fair Value Hierarchy Classification) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities held in trusts	$ 965	$ 881
Short-term borrowings	(206)	(247)
Portion at Other than Fair Value Measurement [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Customer financing notes receivable	299	271
Short-term borrowings	(206)	(247)
Long-term debt (excluding finance leases)	(30,942)	(31,512)
Long-term liabilities	(35)	(27)
Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities held in trusts	965	881
Derivative assets	103	241
Derivative liabilities	(133)	(98)
Customer financing notes receivable	326	264
Short-term borrowings	(206)	(247)
Long-term debt (excluding finance leases)	(36,200)	(38,615)
Long-term liabilities	(33)	(25)
Fair Value Level 1 [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities held in trusts	890	773
Derivative assets	0	0
Derivative liabilities	0	0
Customer financing notes receivable	0	0
Short-term borrowings	0	0
Long-term debt (excluding finance leases)	0	0
Long-term liabilities	0	0
Fair Value Level 2 [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities held in trusts	75	108
Derivative assets	103	241
Derivative liabilities	(133)	(98)
Customer financing notes receivable	326	264
Short-term borrowings	(160)	(160)
Long-term debt (excluding finance leases)	(36,147)	(38,540)
Long-term liabilities	(33)	(25)
Fair Value Level 3 [Member] | Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities held in trusts	0	0
Derivative assets	0	0
Derivative liabilities	0	0
Customer financing notes receivable	0	0
Short-term borrowings	(46)	(87)
Long-term debt (excluding finance leases)	(53)	(75)
Long-term liabilities	$ 0	$ 0