Condensed Consolidating Financial Information (Statement of Income) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Revenues and Other Income
Sales and other operating revenues	$ 20,878	$ 23,103
Equity in earnings (losses) of affiliates	365	516
Net gain on dispositions	1	1
Other income (loss)	0	38
Total Revenues and Other Income	21,244	23,658
Costs and Expenses
Purchased crude oil and products	18,440	21,055
Operating expenses	1,341	1,307
Selling, general and administrative expenses	319	366
Depreciation and amortization	342	331
Impairments	3,006	1
Taxes other than income taxes	157	128
Accretion on discounted liabilities	6	6
Interest and debt expense	111	119
Foreign currency transaction (gains) losses	0	5
Total Costs and Expenses	23,722	23,318
Income (loss) before income taxes	(2,478)	340
Income tax benefit	(51)	70
Net Income (Loss)	(2,427)	270
Less: net income attributable to noncontrolling interests	69	66
Net Income (Loss) Attributable to Phillips 66	(2,496)	204
Comprehensive Loss	(2,635)	342
Phillips 66
Revenues and Other Income
Total Revenues and Other Income	(2,420)	281
Phillips 66 Company
Revenues and Other Income
Total Revenues and Other Income	16,078	19,027
All Other Subsidiaries
Revenues and Other Income
Total Revenues and Other Income	8,027	9,087
Reportable Legal Entities | Phillips 66
Revenues and Other Income
Sales and other operating revenues	0	0
Equity in earnings (losses) of affiliates	(2,420)	281
Net gain on dispositions	0	0
Other income (loss)	0	0
Costs and Expenses
Purchased crude oil and products	0	0
Operating expenses	0	0
Selling, general and administrative expenses	3	3
Depreciation and amortization	0	0
Impairments	0	0
Taxes other than income taxes	0	0
Accretion on discounted liabilities	0	0
Interest and debt expense	78	93
Foreign currency transaction (gains) losses		0
Total Costs and Expenses	81	96
Income (loss) before income taxes	(2,501)	185
Income tax benefit	(5)	(19)
Net Income (Loss)	(2,496)	204
Less: net income attributable to noncontrolling interests	0	0
Net Income (Loss) Attributable to Phillips 66	(2,496)	204
Comprehensive Loss	(2,704)	276
Reportable Legal Entities | Phillips 66 Company
Revenues and Other Income
Sales and other operating revenues	15,510	17,415
Equity in earnings (losses) of affiliates	(361)	431
Net gain on dispositions	1	0
Other income (loss)	(2)	20
Costs and Expenses
Purchased crude oil and products	14,986	17,080
Operating expenses	1,117	1,000
Selling, general and administrative expenses	211	255
Depreciation and amortization	235	227
Impairments	1,805	0
Taxes other than income taxes	123	95
Accretion on discounted liabilities	5	4
Interest and debt expense	36	36
Foreign currency transaction (gains) losses		0
Total Costs and Expenses	18,518	18,697
Income (loss) before income taxes	(2,440)	330
Income tax benefit	(20)	49
Net Income (Loss)	(2,420)	281
Less: net income attributable to noncontrolling interests	0	0
Net Income (Loss) Attributable to Phillips 66	(2,420)	281
Comprehensive Loss	(2,628)	353
Reportable Legal Entities | All Other Subsidiaries
Revenues and Other Income
Sales and other operating revenues	5,368	5,688
Equity in earnings (losses) of affiliates	239	165
Net gain on dispositions	0	1
Other income (loss)	2	18
Costs and Expenses
Purchased crude oil and products	6,689	8,254
Operating expenses	254	326
Selling, general and administrative expenses	107	110
Depreciation and amortization	107	104
Impairments	1,201	1
Taxes other than income taxes	34	33
Accretion on discounted liabilities	1	1
Interest and debt expense	78	67
Foreign currency transaction (gains) losses		5
Total Costs and Expenses	8,471	8,901
Income (loss) before income taxes	(444)	186
Income tax benefit	(26)	40
Net Income (Loss)	(418)	146
Less: net income attributable to noncontrolling interests	69	66
Net Income (Loss) Attributable to Phillips 66	(487)	80
Comprehensive Loss	(627)	211
Consolidating Adjustments
Revenues and Other Income
Sales and other operating revenues	(3,348)	(4,376)
Equity in earnings (losses) of affiliates	2,907	(361)
Net gain on dispositions	0	0
Other income (loss)	0	0
Total Revenues and Other Income	(441)	(4,737)
Costs and Expenses
Purchased crude oil and products	(3,235)	(4,279)
Operating expenses	(30)	(19)
Selling, general and administrative expenses	(2)	(2)
Depreciation and amortization	0	0
Impairments	0	0
Taxes other than income taxes	0	0
Accretion on discounted liabilities	0	1
Interest and debt expense	(81)	(77)
Foreign currency transaction (gains) losses		0
Total Costs and Expenses	(3,348)	(4,376)
Income (loss) before income taxes	2,907	(361)
Income tax benefit	0	0
Net Income (Loss)	2,907	(361)
Less: net income attributable to noncontrolling interests	0	0
Net Income (Loss) Attributable to Phillips 66	2,907	(361)
Comprehensive Loss	3,324	(498)
Consolidating Adjustments | Phillips 66
Revenues and Other Income
Sales and other operating revenues	0	0
Consolidating Adjustments | Phillips 66 Company
Revenues and Other Income
Sales and other operating revenues	930	1,161
Consolidating Adjustments | All Other Subsidiaries
Revenues and Other Income
Sales and other operating revenues	$ 2,418	$ 3,215