Variable Annuity Reinsurance (Details)	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended			3 Months Ended		9 Months Ended																3 Months Ended	9 Months Ended					3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended	9 Months Ended	3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2011 USD ($) rating state	Sep. 30, 2010 USD ($)	Sep. 30, 2011 USD ($) rating state	Sep. 30, 2010 USD ($)	Sep. 30, 2011 WM Life Re USD ($)	Sep. 30, 2010 WM Life Re USD ($)	Sep. 30, 2011 WM Life Re USD ($)	Sep. 30, 2010 WM Life Re USD ($)	Dec. 31, 2010 WM Life Re USD ($)	Sep. 30, 2011 WM Life Re Variable annuity reinsurance. USD ($)	Sep. 30, 2010 WM Life Re Variable annuity reinsurance. USD ($)	Sep. 30, 2011 WM Life Re Variable annuity reinsurance. USD ($)	Sep. 30, 2010 WM Life Re Variable annuity reinsurance. USD ($)	Sep. 30, 2011 WM Life Re Cash. USD ($)	Dec. 31, 2010 WM Life Re Cash. USD ($)	Sep. 30, 2011 WM Life Re Fixed maturity investments USD ($)	Dec. 31, 2010 WM Life Re Fixed maturity investments USD ($)	Sep. 30, 2011 WM Life Re Short-term investments USD ($)	Dec. 31, 2010 WM Life Re Short-term investments USD ($)	Sep. 30, 2011 WM Life Re Citigroup USD ($)	Sep. 30, 2011 WM Life Re Royal Bank of Scotland USD ($)	Sep. 30, 2011 WM Life Re Bank of America USD ($)	Sep. 30, 2011 WM Life Re Barclays USD ($)	Sep. 30, 2011 WM Life Re Nomura USD ($)	Sep. 30, 2011 WM Life Re JP Morgan USD ($)	Sep. 30, 2011 WM Life Re BNP Paribas USD ($)	Sep. 30, 2011 WM Life Re Goldman Sachs USD ($)	Sep. 30, 2011 Level 3 Inputs Variable annuity reinsurance. USD ($)	Sep. 30, 2011 Level 3 Inputs Variable annuity reinsurance. USD ($)	Sep. 30, 2011 Variable annuity reinsurance. USD ($)	Sep. 30, 2011 Variable annuity reinsurance. JPY (¥)	Dec. 31, 2010 Variable annuity reinsurance. USD ($)	Dec. 31, 2010 Variable annuity reinsurance. JPY (¥)	Sep. 30, 2011 Level 1 Inputs USD ($)	Sep. 30, 2011 Level 1 Inputs USD ($)	Sep. 30, 2011 Level 2 Inputs USD ($)	Sep. 30, 2011 Level 2 Inputs USD ($)	Sep. 30, 2011 Level 3 Inputs USD ($)	Sep. 30, 2011 Level 3 Inputs USD ($)	Sep. 30, 2011 Fair Value USD ($)	Sep. 30, 2011 Fair Value USD ($)	Sep. 30, 2011 Fixed income/Interest rate USD ($)	Sep. 30, 2010 Fixed income/Interest rate USD ($)	Sep. 30, 2011 Fixed income/Interest rate USD ($)	Sep. 30, 2010 Fixed income/Interest rate USD ($)	Sep. 30, 2011 Foreign exchange USD ($)	Sep. 30, 2010 Foreign exchange USD ($)	Sep. 30, 2011 Foreign exchange USD ($)	Sep. 30, 2010 Foreign exchange USD ($)	Sep. 30, 2011 Equity USD ($)	Sep. 30, 2010 Equity USD ($)	Sep. 30, 2011 Equity USD ($)	Sep. 30, 2010 Equity USD ($)
Variable annuity reinsurance
Total guarantee value																														$ 3,000,000,000	¥ 234,500,000,000	$ 2,900,000,000	¥ 237,400,000,000
Collective account values of underlying variable annuities as a percentage of the guarantee value (as a percent)																														78.00%	78.00%	82.00%	82.00%
Pre-tax operating results of WM Life Re
Fees, included in other revenues					8,400,000	7,700,000	24,300,000	22,300,000
Change in fair value of variable annuity liability, included in other revenues										(164,400,000)	(53,500,000)	(148,000,000)	(204,700,000)
Change in fair value of derivatives, included in other revenues					148,900,000	(15,700,000)	105,400,000	114,700,000																										27,600,000	10,800,000	75,700,000	67,500,000	45,600,000	27,100,000	148,900,000	105,400,000	29,800,000	(25,500,000)	17,300,000	(1,900,000)	63,000,000	33,000,000	32,800,000	99,600,000	56,100,000	(23,200,000)	55,300,000	17,000,000
Foreign exchange, included in other revenues					14,800,000	10,400,000	17,100,000	16,000,000
Other investment income and gains (losses)					500,000	(200,000)	(100,000)	(700,000)
Total revenues	501,300,000	551,000,000	1,584,500,000	2,013,900,000	8,200,000	(51,300,000)	(1,300,000)	(52,400,000)
Change in fair value of variable annuity death benefit liabilities, included in other expenses										(5,600,000)	300,000	(3,100,000)	(5,800,000)
Death benefit claims paid, included in other expenses					(700,000)	(600,000)	(2,400,000)	(1,400,000)
General and administrative expenses	(36,200,000)	(32,100,000)	(120,400,000)	(119,500,000)	(1,100,000)	(1,400,000)	(3,200,000)	(5,000,000)
Pre-tax income (loss) from continuing operations	1,200,000	75,200,000	3,600,000	57,500,000	800,000	(53,000,000)	(10,000,000)	(64,600,000)
Changes in variable annuity liabilities
Balance of liabilities, at the beginning of the period																												(591,300,000)	(610,200,000)
Realized and unrealized gains (losses)																												(170,000,000)	(151,100,000)
Balance of liabilities, at the end of the period																												(761,300,000)	(761,300,000)
Changes in derivative instruments
Balance of assets, at the beginning of the period																																		(11,900,000)		48,200,000	72,200,000	232,700,000	275,300,000	269,000,000	347,500,000			43,900,000				225,300,000				78,300,000
Purchases																																							5,000,000		5,000,000
Realized and unrealized gains (losses)					148,900,000	(15,700,000)	105,400,000	114,700,000																										27,600,000	10,800,000	75,700,000	67,500,000	45,600,000	27,100,000	148,900,000	105,400,000	29,800,000	(25,500,000)	17,300,000	(1,900,000)	63,000,000	33,000,000	32,800,000	99,600,000	56,100,000	(23,200,000)	55,300,000	17,000,000
Sales/settlements																																		(15,700,000)	(10,800,000)	(48,400,000)	(64,200,000)		(29,100,000)	(64,100,000)	(104,100,000)
Balance of assets, at the end of the period																																				75,500,000	75,500,000	278,300,000	278,300,000	353,800,000	353,800,000	50,300,000		50,300,000		212,000,000		212,000,000		91,500,000		91,500,000
Realized and unrealized derivative gains (losses) recognized in other revenues and carrying values of instruments
Realized and unrealized derivative gains (losses) recognized in other revenues					148,900,000	(15,700,000)	105,400,000	114,700,000																										27,600,000	10,800,000	75,700,000	67,500,000	45,600,000	27,100,000	148,900,000	105,400,000	29,800,000	(25,500,000)	17,300,000	(1,900,000)	63,000,000	33,000,000	32,800,000	99,600,000	56,100,000	(23,200,000)	55,300,000	17,000,000
Carrying Value																																				75,500,000	75,500,000	278,300,000	278,300,000	353,800,000	353,800,000	50,300,000		50,300,000		212,000,000		212,000,000		91,500,000		91,500,000
Credit risk on derivative instruments
OTC derivative instruments					363,400,000		363,400,000		351,500,000
Collateral held					(130,300,000)		(130,300,000)		(101,000,000)							(58,100,000)	(48,600,000)	(72,200,000)	(52,400,000)
Collateral provided					22,600,000		22,600,000		25,300,000
Net exposure to credit losses on fair value of OTC instruments					255,700,000		255,700,000		275,800,000											46,700,000	86,500,000	49,700,000	32,200,000	15,600,000	14,700,000	7,500,000	2,800,000
Number of creditworthiness ratings	21		21
Additional collateral					419,700,000		419,700,000		326,000,000					393,300,000	291,100,000	11,900,000	3,300,000	14,500,000	31,600,000
Adjustments for counterparty credit risk					$ (9,600,000)		$ (9,600,000)		$ (4,000,000)