Condensed Consolidating Financial Information (Income Statement) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenues and Other Income
Sales and Other Operating Revenues	$ (29,125)	$ (27,218)	$ (27,847)	$ (23,103)	$ (29,098)	$ (29,788)	$ (28,980)	$ (23,595)	$ (107,293)	$ (111,461)
Sales and other operating revenues											$ (102,354)
Equity in earnings of affiliates									2,127	2,676	1,732
Net gain on dispositions									20	19	15
Other income									119	61	521
Total Revenues and Other Income									109,559	114,217	104,622
Costs and Expenses
Purchased crude oil and products									95,529	97,930	79,409
Operating expenses									5,074	4,880	4,699
Selling, general and administrative expenses									1,681	1,677	1,695
Depreciation and amortization									1,341	1,356	1,318
Impairments									861	8	24
Taxes other than income taxes									409	425
Taxes other than income taxes											13,462
Accretion on discounted liabilities									23	23	22
Interest and debt expense									458	504	438
Foreign currency transaction gains (losses)									5	(31)	0
Total Costs and Expenses									105,381	106,772	101,067
Income before income taxes									4,178	7,445	3,555
Income tax expense (benefit)									801	1,572	(1,693)
Net Income	810	793	1,504	270	2,316	1,568	1,404	585	3,377	5,873	5,248
Less: net income attributable to noncontrolling interests									301	278	142
Net Income Attributable to Phillips 66	$ 736	$ 712	$ 1,424	$ 204	$ 2,240	$ 1,492	$ 1,339	$ 524	3,076	5,595	5,106
Comprehensive Income									3,370	5,798	5,626
Reportable Legal Entities | Phillips 66
Revenues and Other Income
Sales and Other Operating Revenues									0	0
Sales and other operating revenues											0
Equity in earnings of affiliates									3,342	5,918	5,336
Net gain on dispositions									0	0	0
Other income									0	0	3
Total Revenues and Other Income									3,342	5,918	5,339
Costs and Expenses
Purchased crude oil and products									0	0	0
Operating expenses									0	0	0
Selling, general and administrative expenses									6	7	7
Depreciation and amortization									0	0	0
Impairments									0	0	0
Taxes other than income taxes									0	0
Taxes other than income taxes											0
Accretion on discounted liabilities									0	0	0
Interest and debt expense									347	402	348
Foreign currency transaction gains (losses)									0	0
Total Costs and Expenses									353	409	355
Income before income taxes									2,989	5,509	4,984
Income tax expense (benefit)									(87)	(86)	(122)
Net Income									3,076	5,595	5,106
Less: net income attributable to noncontrolling interests									0	0	0
Net Income Attributable to Phillips 66									3,076	5,595	5,106
Comprehensive Income									3,069	5,520	5,484
Reportable Legal Entities | Phillips 66 Company
Revenues and Other Income
Sales and Other Operating Revenues									(82,857)	(85,486)
Sales and other operating revenues											(74,640)
Equity in earnings of affiliates									2,163	4,030	3,256
Net gain on dispositions									0	8	1
Other income									76	33	471
Total Revenues and Other Income									88,900	93,050	79,978
Costs and Expenses
Purchased crude oil and products									78,244	79,559	63,812
Operating expenses									4,005	3,769	3,672
Selling, general and administrative expenses									1,299	1,297	1,300
Depreciation and amortization									918	926	892
Impairments									3	3	20
Taxes other than income taxes									293	321
Taxes other than income taxes											5,784
Accretion on discounted liabilities									18	18	17
Interest and debt expense									145	146	70
Foreign currency transaction gains (losses)									0	0
Total Costs and Expenses									84,925	86,039	75,567
Income before income taxes									3,975	7,011	4,411
Income tax expense (benefit)									633	1,093	(925)
Net Income									3,342	5,918	5,336
Less: net income attributable to noncontrolling interests									0	0	0
Net Income Attributable to Phillips 66									3,342	5,918	5,336
Comprehensive Income									3,335	5,843	5,714
Reportable Legal Entities | All Other Subsidiaries
Revenues and Other Income
Sales and Other Operating Revenues									(24,436)	(25,975)
Sales and other operating revenues											(27,714)
Equity in earnings of affiliates									738	747	559
Net gain on dispositions									20	11	14
Other income									43	28	47
Total Revenues and Other Income									39,607	40,846	41,791
Costs and Expenses
Purchased crude oil and products									35,067	35,563	30,379
Operating expenses									1,141	1,193	1,085
Selling, general and administrative expenses									386	383	399
Depreciation and amortization									423	430	426
Impairments									858	5	4
Taxes other than income taxes									116	104
Taxes other than income taxes											7,678
Accretion on discounted liabilities									5	5	5
Interest and debt expense									276	250	236
Foreign currency transaction gains (losses)									5	(31)
Total Costs and Expenses									38,277	37,902	40,212
Income before income taxes									1,330	2,944	1,579
Income tax expense (benefit)									255	565	(646)
Net Income									1,075	2,379	2,225
Less: net income attributable to noncontrolling interests									301	278	142
Net Income Attributable to Phillips 66									774	2,101	2,083
Comprehensive Income									1,098	2,291	2,498
Consolidating Adjustments
Revenues and Other Income
Sales and Other Operating Revenues									(18,174)	(17,578)
Sales and other operating revenues											(15,067)
Equity in earnings of affiliates									(4,116)	(8,019)	(7,419)
Net gain on dispositions									0	0	0
Other income									0	0	0
Total Revenues and Other Income									(22,290)	(25,597)	(22,486)
Costs and Expenses
Purchased crude oil and products									(17,782)	(17,192)	(14,782)
Operating expenses									(72)	(82)	(58)
Selling, general and administrative expenses									(10)	(10)	(11)
Depreciation and amortization									0	0	0
Impairments									0	0	0
Taxes other than income taxes									0	0
Taxes other than income taxes											0
Accretion on discounted liabilities									0	0	0
Interest and debt expense									(310)	(294)	(216)
Foreign currency transaction gains (losses)									0	0
Total Costs and Expenses									(18,174)	(17,578)	(15,067)
Income before income taxes									(4,116)	(8,019)	(7,419)
Income tax expense (benefit)									0	0	0
Net Income									(4,116)	(8,019)	(7,419)
Less: net income attributable to noncontrolling interests									0	0	0
Net Income Attributable to Phillips 66									(4,116)	(8,019)	(7,419)
Comprehensive Income									(4,132)	(7,856)	(8,070)
Consolidating Adjustments | Phillips 66
Revenues and Other Income
Sales and Other Operating Revenues									0	0
Sales and other operating revenues											0
Consolidating Adjustments | Phillips 66 Company
Revenues and Other Income
Sales and Other Operating Revenues									3,804	3,493
Sales and other operating revenues											1,610
Consolidating Adjustments | All Other Subsidiaries
Revenues and Other Income
Sales and Other Operating Revenues									$ 14,370	$ 14,085
Sales and other operating revenues											$ 13,457