Reinsurance - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014 Reinsurer	Dec. 31, 2013	Dec. 31, 2012
Effects of Reinsurance [Line Items]
Reinsurance recoverables included in other long-term assets	$ 646us-gaap_ReinsuranceRecoverables	$ 578us-gaap_ReinsuranceRecoverables
Percentage of reinsurance recoverables resulting from 100% coinsurance agreements	45.00%	37.00%
Premiums ceded	357us-gaap_CededPremiumsWritten	33us-gaap_CededPremiumsWritten	34us-gaap_CededPremiumsWritten
Benefits ceded	272	70	86
Number of reinsurers comprising other reinsurance recoverables balance	16
Maximum carrying value of reinsurance recoverables for a number of reinsurers	80
Number of reinsurers who have placed cash and securities in trusts	3
Cash and securities in trusts held by certain reinsurers	$ 99
100% Coinsurance Agreements
Effects of Reinsurance [Line Items]
Percentage of coinsurance agreement	100.00%

Amount held in cash and securities in trust, at least equal to the recoverable from the reinsurer

No definition available.

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- Definition

Maximum carrying value of reinsurance recoverables for a number of reinsurers

+ References

No definition available.

+ Details

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- Definition

Number of reinsurers comprising other reinsurance recoverables balance

+ References

No definition available.

+ Details

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- Definition

Number of reinsurers who have placed cash and securities in trusts

+ References

No definition available.

+ Details

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- Definition

Percentage Of Coinsurance Agreement

+ References

No definition available.

+ Details

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- Definition

Amount of written premiums ceded to other entities.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 17

-Article 12

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 605

-Section 50

-Paragraph 1

-Subparagraph (b),(c)(2)

-URI http://asc.fasb.org/extlink&oid=6486672&loc=d3e27261-158547

+ Details

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Balance Type:	debit
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- Details

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- Definition

Amount of reduction of provision for policy benefits and costs incurred for policies ceded.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 20

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6811-158387

+ Details

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- Definition

Amount after valuation allowance recoverable including premium paid under reinsurance contracts. Examples include, but are not limited to, settled and unsettled claims, incurred but not reported losses, loss adjustment expense, premium paid, policy benefits and policy reserves.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 6

-Article 7

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 20

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6480758&loc=d3e6824-158387

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.(a),6)

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

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- Definition

Percentage of total reinsurance recoverables.

+ References

No definition available.

+ Details

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- Details

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