Fair Value Measurement (Fair Value Measurement Inputs) (Details) - USD ($) $ in Millions	Jun. 30, 2017	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other current assets	$ 211	$ 199
Other assets	1,957	1,956
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	80	76
Derivatives:
Derivative Asset	64	132
Derivatives: [Abstract]
Derivative Liability	14	44
Level 1
Investment securities (current and long-term):
Available-for-sale Securities	27	27
Trust Assets Fair Value Disclosure	11	12
Derivatives:
Derivative Asset	5	8
Contingent receivable	0	0
Total assets	43	47
Derivatives: [Abstract]
Derivative Liability	3	2
Discontinued Operation, Contingent Payable		0
Long-term debt, including current portion	0	0
Total liabilities	3	2
Level 2
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Trust Assets Fair Value Disclosure	122	118
Derivatives:
Derivative Asset	139	184
Contingent receivable	0	0
Total assets	261	302
Derivatives: [Abstract]
Derivative Liability	15	56
Discontinued Operation, Contingent Payable		23
Long-term debt, including current portion	14,744	15,196
Total liabilities	14,759	15,275
Level 3
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Trust Assets Fair Value Disclosure	0	0
Derivatives:
Derivative Asset	0	0
Contingent receivable	137	135
Total assets	137	135
Derivatives: [Abstract]
Derivative Liability	0	0
Discontinued Operation, Contingent Payable		0
Long-term debt, including current portion	0	0
Total liabilities	0	0
Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Available-for-sale Securities	52	50
Trust Assets Fair Value Disclosure	188	183
Derivatives:
Derivative Asset	144	192
Contingent receivable	150	150
Derivatives: [Abstract]
Derivative Liability	18	58
Discontinued Operation, Contingent Payable		23
Long-term debt, including current portion	15,354	16,027
Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	52	50
Trust Assets Fair Value Disclosure	188	183
Derivatives:
Derivative Asset	144	192
Contingent receivable	137	135
Total assets	521	560
Derivatives: [Abstract]
Derivative Liability	18	58
Discontinued Operation, Contingent Payable		23
Long-term debt, including current portion	14,744	15,196
Total liabilities	14,762	15,277
Embedded Derivative Financial Instruments [Member]
Derivatives:
Derivative Asset	58	125
Derivatives: [Abstract]
Derivative Liability	10	44
Embedded Derivative Financial Instruments [Member] | Level 1
Derivatives:
Derivative Asset	0	0
Derivatives: [Abstract]
Derivative Liability	0	0
Embedded Derivative Financial Instruments [Member] | Level 2
Derivatives:
Derivative Asset	62	137
Derivatives: [Abstract]
Derivative Liability	14	56
Embedded Derivative Financial Instruments [Member] | Level 3
Derivatives:
Derivative Asset	0	0
Derivatives: [Abstract]
Derivative Liability	0	0
Embedded Derivative Financial Instruments [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset	62	137
Derivatives: [Abstract]
Derivative Liability	14	56
Embedded Derivative Financial Instruments [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset	62	137
Derivatives: [Abstract]
Derivative Liability	14	56
Commodity Contract [Member]
Derivatives:
Derivative Asset	6	7
Derivatives: [Abstract]
Derivative Liability	4	0
Commodity Contract [Member] | Level 1
Derivatives:
Derivative Asset	5	8
Derivatives: [Abstract]
Derivative Liability	3	2
Commodity Contract [Member] | Level 2
Derivatives:
Derivative Asset	1	1
Derivatives: [Abstract]
Derivative Liability	1	0
Commodity Contract [Member] | Level 3
Derivatives:
Derivative Asset	0	0
Derivatives: [Abstract]
Derivative Liability	0	0
Commodity Contract [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset	6	9
Derivatives: [Abstract]
Derivative Liability	4	2
Commodity Contract [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset	6	9
Derivatives: [Abstract]
Derivative Liability	4	2
Africa and onshore California [Member] | Commodity Contract [Member] | Level 1
Derivatives:
Derivative Asset	0	0
Africa and onshore California [Member] | Commodity Contract [Member] | Level 2
Derivatives:
Derivative Asset	76	46
Africa and onshore California [Member] | Commodity Contract [Member] | Level 3
Derivatives:
Derivative Asset	0	0
Africa and onshore California [Member] | Commodity Contract [Member] | Carrying Amount, Fair Value Disclosure [Member]
Derivatives:
Derivative Asset	76	46
Africa and onshore California [Member] | Commodity Contract [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset	76	46
U.S. core fixed income fund [Member] | Level 1
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Trust Assets Fair Value Disclosure	0	0
U.S. core fixed income fund [Member] | Level 2
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Trust Assets Fair Value Disclosure	0	0
U.S. core fixed income fund [Member] | Level 3
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Trust Assets Fair Value Disclosure	0	0
U.S. core fixed income fund [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Available-for-sale Securities	25	23
Trust Assets Fair Value Disclosure	55	53
U.S. core fixed income fund [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	25	23
Trust Assets Fair Value Disclosure	55	53
Money market funds [Member] | Level 1
Investment securities (current and long-term):
Available-for-sale Securities	22	22
Trust Assets Fair Value Disclosure	11	12
Money market funds [Member] | Level 2
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Trust Assets Fair Value Disclosure	0	0
Money market funds [Member] | Level 3
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Trust Assets Fair Value Disclosure	0	0
Money market funds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Available-for-sale Securities	22	22
Trust Assets Fair Value Disclosure	11	12
Money market funds [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	22	22
Trust Assets Fair Value Disclosure	11	12
Equity securities | Level 1
Investment securities (current and long-term):
Available-for-sale Securities	5	5
Equity securities | Level 2
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Equity securities | Level 3
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Equity securities | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Available-for-sale Securities	5	5
Equity securities | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	5	5
Government bonds | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Government bonds | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	36	36
Government bonds | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Government bonds | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	36	36
Government bonds | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	36	36
Corporate bonds [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Corporate bonds [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	32	32
Corporate bonds [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Corporate bonds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	32	32
Corporate bonds [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	32	32
Government mortgage-backed securities [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Government mortgage-backed securities [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	28	25
Government mortgage-backed securities [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Government mortgage-backed securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	28	25
Government mortgage-backed securities [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	28	25
Asset-backed securities [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Asset-backed securities [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	17	16
Asset-backed securities [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Asset-backed securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	17	16
Asset-backed securities [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	17	16
Collateralized Mortgage Backed Securities [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Collateralized Mortgage Backed Securities [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	8	8
Collateralized Mortgage Backed Securities [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Collateralized Mortgage Backed Securities [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	8	8
Collateralized Mortgage Backed Securities [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	8	8
Municipal bonds [Member] | Level 1
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Municipal bonds [Member] | Level 2
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	1	1
Municipal bonds [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Municipal bonds [Member] | Carrying Amount, Fair Value Disclosure [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	1	1
Municipal bonds [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	1	1
Bank Time Deposits [Member] | Carrying Amount, Fair Value Disclosure [Member]
Fair Value, Assets and Liabilities Measured on Recurring Basis, Financial Statement Captions [Line Items]
Other current assets	34	28
Other assets	122	122
Investment Securities [Member]
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	25	23
Investment Securities [Member] | U.S. core fixed income fund [Member]
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	25	23
Restricted Funds [Member]
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	55	53
Restricted Funds [Member] | U.S. core fixed income fund [Member]
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	$ 55	$ 53