Income Tax Level 4 Deferred tax assets (liabilities) (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Deferred Tax Assets, Net of Valuation Allowance [Abstract]
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Policyholder Liabilities	$ 124	$ 163
Deferred Tax Assets, Tax Deferred Expense, Reserves and Accruals, Loss Reserves	12	0
Deferred Tax Assets, Investments	1,094	1,516
Deferred Tax Assets, Derivative Instruments	44	742
Deferred Tax Assets, Operating Loss Carryforwards	1,116	377
Deferred Tax Assets, Tax Credit Carryforwards, Alternative Minimum Tax	246	327
Deferred Tax Assets, Tax Credit Carryforwards, Foreign	58	44
Deferred Tax Assets, Other	0	71
Deferred Tax Assets, Gross	2,694	3,240
Deferred Tax Assets, Net of Valuation Allowance	1,237	2,110
Components of Deferred Tax Liabilities [Abstract]
Deferred Tax Liabilities, Deferred Expense, Deferred Policy Acquisition Cost	585	650
Deferred Tax Liabilities Net Unrealized gains on Investments	816	403
Deferred Tax Liabilities, Employee Benefits	39	52
Deferred Tax Liabilities Other Depreciable and Amortizable Assets	(1)	(25)
Deferred Tax Liabilities, Other	(16)	0
Deferred Tax Liabilities, Net	1,457	1,130
Deferred Tax Assets, Net	1,237	2,110
Income Taxes Receivable, Current	231	80
Current Income Tax Cumulative Surplus, Benefit	0	0	(18)
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	3,189
Operating Loss Carryforwards		1,076
Expected Tax Benefit Attributable to Net Operating Losses Domestic Near term	$ 7
Earliest Tax Year [Member]
Components of Deferred Tax Liabilities [Abstract]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2013
Latest Tax Year [Member]
Components of Deferred Tax Liabilities [Abstract]
Operating Loss Carryforwards, Expiration Date	Dec. 31, 2029