Debt and Borrowing Arrangements - Schedule of Contractual Debt Maturities (Details) $ in Millions	Dec. 31, 2017 USD ($)
Contractual debt maturities
Within one year	$ 252
Between one and two years	97
Between two and three years	0
Between three and four years	22
Between four and five years	0
Thereafter	0
Total	371
Warehouse Facilities
Contractual debt maturities
Within one year	220
Between one and two years	0
Between two and three years	0
Between three and four years	0
Between four and five years	0
Thereafter	0
Total	220
Servicing Advance Facility
Contractual debt maturities
Within one year	32
Between one and two years	0
Between two and three years	0
Between three and four years	0
Between four and five years	0
Thereafter	0
Total	32
Unsecured debt
Contractual debt maturities
Within one year	0
Between one and two years	97
Between two and three years	0
Between three and four years	22
Between four and five years	0
Thereafter	0
Total	$ 119

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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Amount of long-term debt payable, sinking fund requirements, and other securities issued that are redeemable by holder at fixed or determinable prices and dates maturing after the fifth fiscal year following the latest fiscal year. Excludes interim and annual periods when interim periods are reported on a rolling approach, from latest balance sheet date.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

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