Fair Value Measurement - Quantitative Information about Level 3 Fair Value Measurements of Assets (Detail) - Level 3 - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Fair Value, Measurements, Recurring
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Fair value of assets	$ 69	$ 0
Minimum \| Home Equity Conversion Mortgages \| Fair Value, Measurements, Recurring \| Discounted Cash Flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount spreads (percent)	0.80%
Conditional prepayment rate (percent)	70.00%
Line of credit draw rates (percent)	0.00%
Maximum \| Home Equity Conversion Mortgages \| Discounted Cash Flow
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Discount spreads (percent)	1.50%
Conditional prepayment rate (percent)	100.00%
Line of credit draw rates (percent)	20.00%

Fair Value Inputs, Line of Credit Draw Rates

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- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

+ Details

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- Definition

Rate at which loans or a loan portfolio are expected to prepay principal balances, used as an input to measure fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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