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Segment Information - Schedule of reconciliation of segment income before tax to income from continuing operations before income taxes (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2016 | Sep. 30, 2016 | Jun. 30, 2016 | Mar. 31, 2016 | Dec. 31, 2015 | Sep. 30, 2015 | Jun. 30, 2015 | Mar. 31, 2015 | Dec. 31, 2016 | Dec. 31, 2015 | Dec. 31, 2014
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating income from continuing operations before income taxes | $ 568 | $ 436 | $ 439 | $ 463 | $ 656 | $ 423 | $ 308 | $ 461 | $ 1,906 | $ 1,848 | $ 1,966
Interest income |  |  |  |  |  |  |  |  | 9 | 14 | 10
Interest expense |  |  |  |  |  |  |  |  | (282) | (273) | (255)
Other income |  |  |  |  |  |  |  |  | 36 | 100 | 44
Income before income taxes |  |  |  |  |  |  |  |  | 1,669 | 1,689 | 1,765
Operating Segments |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating income from continuing operations before income taxes |  |  |  |  |  |  |  |  | 2,144 | 2,042 | 2,133
Operating Segments | Risk Solutions |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating income from continuing operations before income taxes |  |  |  |  |  |  |  |  | 1,587 | 1,506 | 1,648
Operating Segments | HR Solutions |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating income from continuing operations before income taxes |  |  |  |  |  |  |  |  | 557 | 536 | 485
Segment Reconciling Items |  |  |  |  |  |  |  |  |  |  |
Segment Reporting Information [Line Items] |  |  |  |  |  |  |  |  |  |  |
Operating income from continuing operations before income taxes |  |  |  |  |  |  |  |  | $ (238) | $ (194) | $ (167)

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- Definition Amount of the cost of borrowed funds accounted for as interest expense. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450988&loc=d3e26243-108391 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=64930785&loc=d3e28555-108399 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.9) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 + Details
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