(Basis of Fair Value Measurements on a Recurring Basis) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	$ 1,569	$ 1,683
Gross	274	336
Long-term debt including debt due within one year	18,661	20,212
Gross	530	425
Government debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	555	700
Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	1,014	983
Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	21	100
Equity securities	15	16
Total assets at fair value	2,507	2,701
Long-term debt including debt due within one year	18,661	20,212
Total liabilities at fair value	19,191	20,637
Fair Value, Measurements, Recurring | Interest rates 6
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	35	0
Fair Value, Measurements, Recurring | Foreign currency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	149	226
Gross	69	149
Fair Value, Measurements, Recurring | Commodities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	90	110
Gross	151	212
Fair Value, Measurements, Recurring | Interest rates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	310	64
Fair Value, Measurements, Recurring | Government debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	555	700
Fair Value, Measurements, Recurring | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	1,014	983
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Items (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	0	0
Equity securities	15	16
Total assets at fair value	60	33
Long-term debt including debt due within one year	0	0
Total liabilities at fair value	14	23
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Items (Level 1) | Interest rates 6
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Items (Level 1) | Foreign currency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	0	0
Gross	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Items (Level 1) | Commodities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	23	17
Gross	14	23
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Items (Level 1) | Interest rates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Items (Level 1) | Government debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	0	0
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Items (Level 1) | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	22	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Marketable securities	21	100
Equity securities	0	0
Total assets at fair value	2,447	2,668
Long-term debt including debt due within one year	18,661	20,212
Total liabilities at fair value	19,177	20,614
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rates 6
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	35	0
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign currency
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	149	226
Gross	69	149
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Commodities
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	67	93
Gross	137	189
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rates
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gross	310	64
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Government debt
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	555	700
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt securities	992	983
Held-to-maturity Securities [Member] | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	220	410
Held-to-maturity Securities [Member] | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Items (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Held-to-maturity Securities [Member] | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	220	410
Money Market Funds [Member] | Fair Value, Measurements, Recurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	408	156
Money Market Funds [Member] | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Items (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	0	0
Money Market Funds [Member] | Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash equivalents	$ 408	$ 156