Income Taxes - Differences Between Statutory Income Tax Rate and Effective Income Tax Rate (Detail) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ (11)	$ 97
Increase (decrease) resulting from:
Tax-exempt income from municipal bonds	(5)	(9)
Dividend received exclusion	(3)	(8)
Other	0	(5)
Total provision (benefit) for income taxes	$ (19)	$ 75
Tax at statutory rate	21.00%	35.00%
Increase (decrease) resulting from:
Tax-exempt income from municipal bonds	10.00%	(3.30%)
Dividend received exclusion	6.00%	(2.90%)
Other	1.00%	(1.60%)
Provision for income taxes	38.00%	27.20%

Percentage of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 740
-SubTopic 10
-Section 50
-Paragraph 13
-URI http://asc.fasb.org/extlink&oid=84230637&loc=d3e32698-109319

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-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

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Percentage of domestic federal statutory tax rate applicable to pretax income (loss).

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Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to deduction for dividend.

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