Income Taxes (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Current Income Taxes [Abstract]
U.S. income		$ 604	$ 320	$ 267
Foreign income		72	58	45
State income		43	20	19
Deferred Income Taxes [Abstract]
Deferred Federal Tax Expense Benefit		131	193	187
Deferred Foreign Tax Expense Benefit		4	23	8
Deferred State And Local Tax Expense Benefit		(1)	1	(7)
Reconciliation of total taxes to nominal federal rate details [Abstract]
Effective Income Tax Rate Reconciliation At Federal Statutory Income Amount		867	657	631
Effective Income Tax Rate Reconciliation Tax Exempt Income Amount		(28)	(29)	(31)
Effective Income Tax Rate Reconciliation Deductions Dividends Amount		(3)	(4)	(3)
Effective Income Tax Rate Reconciliation Tax Settlements Domestic Amount		0	(30)	0
Effective Income Tax Rate Reconciliation State And Local Income Taxes Amount		28	14	9
Effective Income Tax Rate Reconciliation Change In Deferred Tax Assets Valuation Allowance Amount		6	5	(93)
Effective Income Tax Rate Reconciliation Other Adjustments Amount		20	19	17
Total taxes		853	615	519
Deferred tax assets [Abstract]
Employee and retiree benefit plans		765	829
Investments, net		95	108
Other insurance and contractholder liabilities		486	443
Deferred gain on sale of business		28	46
Policy acquisition expenses		147	151
Loss carryforwards		9	8
Other accrued liabilities		164	109
Bad debt expense		21	17
Other		33	37
Deferred tax assets before valuation allowance		1,748	1,748
Valuation allowance for deferred tax assets		(42)	(45)
Deferred tax assets, net of valuation allowance		1,706	1,703
Deferred tax liabilities [Abstract]
Depreciation and amortization		704	377
Foreign operations, net		147	128
Unrealized appreciation (depreciation) on investments and foreign currency translation		481	395
Total deferred tax liabilities		1,332	900
Net deferred income tax assets		374	803
Reconciliation of unrecognized tax benefits details [Abstract]
Balance at January 1,	52	52	177	214
Increase (decrease) due to prior year positions		(5)	(113)	(55)
Increase due to current year positions		7	7	34
Reduction in net unrecognized tax benefit resulting from IRS examination		0	(17)	(13)
Reduction related to lapse of applicable statute of limitations		(3)	(2)	(3)
Balance at December 31,		51	52	177
Permanently Invested Foreign Earnings [Line Items]
Increase to shareholders' net income for change in foreign tax practices	13	(37)	(17)	(11)
Unrecognized deferred tax liabilities related to investments in subsidiaries		116
Unrecorded Deferred Tax Liability Recorded to OCI		10
Income Taxes Text Details [Abstract]
Amount included in unrecognized tax benefits that would impact net income if recognized		29
Liability for net interest and penalties		3	2	14
Effect of IRS examination to shareholders' net income			24
Income tax benefit related to IRS examination			33
Pre-tax charge associated with IRS examination			9
Reduction of interest and penalties resulting from IRS examination			11
Unrecognized Tax Benefits Decreases Resulting From Examinations			11
Valuation Allowance [Line Items]
Valuation Allowance, Amount			$ 7