Significant Accounting Policies (Cash Flows) (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
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income	$ 59	$ 58	$ 50	$ 42	$ 53	$ 56	$ 64	$ 137	$ 209	$ 310	$ 440
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of unconsolidated affiliates	$ (11)	$ (9)	$ (15)	$ 0	$ (29)	$ (17)	$ (12)	$ (21)	(35)	(79)	(70)
Deferred income tax (benefit) expense									(14)	26	(322)
Changes in operating assets and liabilities, net of acquired businesses:
Accounts receivable, net of allowances for doubtful accounts									(16)	(203)	92
Contract assets									(31)	25	40
Contract liabilities									19	(60)	(198)
Other assets and liabilities									(84)	(7)	(148)
Total cash flows provided by operating activities									$ 256	165	$ 193
Calculated under Revenue Guidance in Effect before Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income										300
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of unconsolidated affiliates										(75)
Deferred income tax (benefit) expense										25
Changes in operating assets and liabilities, net of acquired businesses:
Accounts receivable, net of allowances for doubtful accounts										130
Contract assets										(286)
Contract liabilities										(77)
Other assets and liabilities										(5)
Total cash flows provided by operating activities										165
Adjustments Due to Topic 606 | Difference between Revenue Guidance in Effect before and after Topic 606
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income										10
Adjustments to reconcile net income to net cash provided by operating activities:
Equity in earnings of unconsolidated affiliates										(4)
Deferred income tax (benefit) expense										1
Changes in operating assets and liabilities, net of acquired businesses:
Accounts receivable, net of allowances for doubtful accounts										(333)
Contract assets										311
Contract liabilities										17
Other assets and liabilities										(2)
Total cash flows provided by operating activities										$ 0