Quarterly Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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
Condensed Financial Statements, Captions [Line Items]
Total revenues	$ 1,452	$ 1,425	$ 1,422	$ 1,340	$ 1,330	$ 1,278	$ 1,267	$ 1,038	$ 5,639	$ 4,913	$ 4,171
Gross profit	171	169	160	153	157	149	161	117	653	584	439
Equity in earnings of unconsolidated affiliates	11	9	15	0	29	17	12	21	35	79	70
Operating income	88	104	92	78	90	99	100	179	362	468	264
Net income	59	58	50	42	53	56	64	137	209	310	440
Net income attributable to noncontrolling interests	(1)	(2)	(2)	(2)	(6)	(2)	(20)	(1)	(7)	(29)	(8)
Net income attributable to KBR	$ 58	$ 56	$ 48	$ 40	$ 47	$ 54	$ 44	$ 136	$ 202	$ 281	$ 432
Net income attributable to KBR per share:
Net income attributable to KBR per share—Basic (usd per share)	$ 0.41	$ 0.39	$ 0.34	$ 0.28	$ 0.33	$ 0.38	$ 0.31	$ 0.96	$ 1.42	$ 1.99	$ 3.05
Net income attributable to KBR per share—Diluted (usd per share)	$ 0.40	$ 0.39	$ 0.34	$ 0.28	$ 0.33	$ 0.38	$ 0.31	$ 0.96	$ 1.41	$ 1.99	$ 3.05
Aspire
Net income attributable to KBR per share:
Gain on consolidation								$ 108		$ 108