Income Tax Level 4 Deferred tax assets (liabilities) (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Deferred Tax Assets, Net of Valuation Allowance [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Policyholder Liabilities	$ 119	$ 124
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves	4	12
Deferred Tax Assets, Investments	524	1,094
Deferred Tax Assets, Derivative Instruments	90	44
Deferred Tax Assets, Operating Loss Carryforwards	1,166	1,116
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	232	246
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	122	58
Deferred Tax Assets, Other	16	0
Deferred Tax Assets, Gross	2,273	2,694
Deferred Tax Assets, Net of Valuation Allowance, Current	2,273	2,694
Components of Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost	220	585
Deferred Tax Liabilities Net Unrealized gains on Investments	432	816
Deferred Tax Liabilities, Employee Benefits	40	39
Deferred Tax Liabilities Other Depreciable and Amortizable Assets	0	(1)
Deferred Tax Liabilities, Other	0	(16)
Deferred Tax Liabilities, Net	692	1,457
Deferred Tax Assets, Net	1,581	1,237
Income Taxes Receivable, Current	276	231
Current Income Tax Cumulative Surplus, Benefit	$ 0	0	$ 0
Valuation Allowance, Deferred Tax Asset, Explanation of Change	The Company believes it is more likely than not the deferred tax assets will be fully realized. Consequently no valuation allowance has been provided. In assessing the need for a valuation allowance, management considered future taxable temporary difference reversals, future taxable income exclusive of reversing temporary differences and carryovers, taxable income in open carry back years and other tax planning strategies. From time to time, tax planning strategies could include holding a portion of debt securities with market value losses until recovery, altering the level of tax exempt securities held, making investments which have specific tax characteristics, and business considerations such as asset-liability matching.
Deferred Tax Assets, Operating Loss Carryforwards, Subject to Expiration	$ 3,333
Operating Loss Carryforwards		$ 3,189
Expected Tax Benefit Attributable to Net Operating Losses Domestic Near term	$ 3,331
Latest Tax Year [Member]
Components of Deferred Tax Liabilities [Abstract]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2033