Fair Value Measurement (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	$ 78	$ 76
Derivatives:
Derivative Asset	26	132
Derivatives: [Abstract]
Derivative Liability	4	44
Other current assets	196	199
Other assets	2,010	1,956
Level 1
Investment securities (current and long-term):
Available-for-sale Securities	27	27
Trust Assets Fair Value Disclosure	12	12
Derivatives:
Derivative Asset	5	8
Contingent receivable	0	0
Total assets	44	47
Derivatives: [Abstract]
Derivative Liability	1	2
Discontinued Operation, Contingent Payable	0	0
Long-term debt, including current portion	0	0
Total liabilities	1	2
Level 2
Investment securities (current and long-term):
Available-for-sale Securities	0	0
Trust Assets Fair Value Disclosure	118	118
Derivatives:
Derivative Asset	97	184
Contingent receivable	0	0
Total assets	215	302
Derivatives: [Abstract]
Derivative Liability	7	56
Discontinued Operation, Contingent Payable	10	23
Long-term debt, including current portion	14,624	15,196
Total liabilities	14,641	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	135	135
Total assets	135	135
Derivatives: [Abstract]
Derivative Liability	0	0
Discontinued Operation, Contingent Payable	0	0
Long-term debt, including current portion	0	0
Total liabilities	0	0
Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	51	50
Trust Assets Fair Value Disclosure	184	183
Derivatives:
Derivative Asset	102	192
Contingent receivable	135	135
Total assets	472	560
Derivatives: [Abstract]
Derivative Liability	8	58
Discontinued Operation, Contingent Payable	10	23
Long-term debt, including current portion	14,624	15,196
Total liabilities	14,642	15,277
Reported Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	51	50
Trust Assets Fair Value Disclosure	184	183
Derivatives:
Derivative Asset	102	192
Contingent receivable	150	150
Derivatives: [Abstract]
Derivative Liability	8	58
Discontinued Operation, Contingent Payable	10	23
Long-term debt, including current portion	15,363	16,027
Embedded Derivative Financial Instruments [Member]
Derivatives:
Derivative Asset	21	125
Derivatives: [Abstract]
Derivative Liability	4	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	24	137
Derivatives: [Abstract]
Derivative Liability	7	56
Embedded Derivative Financial Instruments [Member] | Level 3
Derivatives:
Derivative Asset	0	0
Derivatives: [Abstract]
Derivative Liability	0	0
Embedded Derivative Financial Instruments [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset	24	137
Derivatives: [Abstract]
Derivative Liability	7	56
Embedded Derivative Financial Instruments [Member] | Reported Value Measurement [Member]
Derivatives:
Derivative Asset	24	137
Derivatives: [Abstract]
Derivative Liability	7	56
Commodity Contract [Member]
Derivatives:
Derivative Asset	5	7
Derivatives: [Abstract]
Derivative Liability	0	0
Commodity Contract [Member] | Level 1
Derivatives:
Derivative Asset	5	8
Derivatives: [Abstract]
Derivative Liability	1	2
Commodity Contract [Member] | Level 2
Derivatives:
Derivative Asset	1	1
Derivatives: [Abstract]
Derivative Liability	0	0
Commodity Contract [Member] | Level 3
Derivatives:
Derivative Asset	0	0
Derivatives: [Abstract]
Derivative Liability	0	0
Commodity Contract [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset	6	9
Derivatives: [Abstract]
Derivative Liability	1	2
Commodity Contract [Member] | Reported Value Measurement [Member]
Derivatives:
Derivative Asset	6	9
Derivatives: [Abstract]
Derivative Liability	1	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	72	46
Africa and onshore California [Member] | Commodity Contract [Member] | Level 3
Derivatives:
Derivative Asset	0	0
Africa and onshore California [Member] | Commodity Contract [Member] | Estimate of Fair Value Measurement [Member]
Derivatives:
Derivative Asset	72	46
Africa and onshore California [Member] | Commodity Contract [Member] | Reported Value Measurement [Member]
Derivatives:
Derivative Asset	72	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] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	24	23
Trust Assets Fair Value Disclosure	54	53
U.S. core fixed income fund [Member] | Reported Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	24	23
Trust Assets Fair Value Disclosure	54	53
Money market funds [Member] | Level 1
Investment securities (current and long-term):
Available-for-sale Securities	22	22
Trust Assets Fair Value Disclosure	12	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] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	22	22
Trust Assets Fair Value Disclosure	12	12
Money market funds [Member] | Reported Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	22	22
Trust Assets Fair Value Disclosure	12	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 | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Available-for-sale Securities	5	5
Equity securities | Reported 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 | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	36	36
Government bonds | Reported Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	36	36
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	24	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] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	24	25
Government mortgage-backed securities [Member] | Reported Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	24	25
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] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	32	32
Corporate bonds [Member] | Reported Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	32	32
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	18	16
Asset-backed securities [Member] | Level 3
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	0	0
Asset-backed securities [Member] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	18	16
Asset-backed securities [Member] | Reported Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	18	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	7	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] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	7	8
Collateralized Mortgage Backed Securities [Member] | Reported Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	7	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] | Estimate of Fair Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	1	1
Municipal bonds [Member] | Reported Value Measurement [Member]
Investment securities (current and long-term):
Trust Assets Fair Value Disclosure	1	1
Bank Time Deposits [Member] | Reported Value Measurement [Member]
Derivatives: [Abstract]
Other current assets	32	28
Other assets	122	122
Restricted Funds [Member]
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	54	53
Restricted Funds [Member] | U.S. core fixed income fund [Member]
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	54	53
Investment Securities [Member]
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	24	23
Investment Securities [Member] | U.S. core fixed income fund [Member]
Investment securities (current and long-term):
Alternative Investments, Fair Value Disclosure	24	23
Other Current Assets
Derivatives:
Derivative Asset	6	7
Derivatives: [Abstract]
Derivative Liability	$ 0	$ 0