Variable Annuity Reinsurance (Details)	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended														3 Months Ended	6 Months Ended					3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2011 USD ($)	Jun. 30, 2010 USD ($)	Jun. 30, 2011 USD ($)	Jun. 30, 2010 USD ($)	Jun. 30, 2011 WM Life Re USD ($)	Jun. 30, 2010 WM Life Re USD ($)	Jun. 30, 2011 WM Life Re USD ($)	Jun. 30, 2010 WM Life Re USD ($)	Dec. 31, 2010 WM Life Re USD ($)	Jun. 30, 2011 WM Life Re Variable annuity reinsurance. USD ($)	Jun. 30, 2010 WM Life Re Variable annuity reinsurance. USD ($)	Jun. 30, 2011 WM Life Re Variable annuity reinsurance. USD ($)	Jun. 30, 2010 WM Life Re Variable annuity reinsurance. USD ($)	Jun. 30, 2011 WM Life Re Cash. USD ($)	Dec. 31, 2010 WM Life Re Cash. USD ($)	Jun. 30, 2011 WM Life Re Fixed maturity investments USD ($)	Dec. 31, 2010 WM Life Re Fixed maturity investments USD ($)	Jun. 30, 2011 WM Life Re Short-term investments USD ($)	Dec. 31, 2010 WM Life Re Short-term investments USD ($)	Jun. 30, 2011 WM Life Re Citigroup USD ($)	Jun. 30, 2011 WM Life Re Royal Bank of Scotland USD ($)	Jun. 30, 2011 WM Life Re Bank of America USD ($)	Jun. 30, 2011 WM Life Re Barclays USD ($)	Jun. 30, 2011 WM Life Re Goldman Sachs USD ($)	Jun. 30, 2011 WM Life Re Other. USD ($)	Jun. 30, 2011 Level 3 Inputs Variable annuity reinsurance. USD ($)	Jun. 30, 2011 Level 3 Inputs Variable annuity reinsurance. USD ($)	Jun. 30, 2011 Variable annuity reinsurance. USD ($)	Jun. 30, 2011 Variable annuity reinsurance. JPY (¥)	Dec. 31, 2010 Variable annuity reinsurance. USD ($)	Dec. 31, 2010 Variable annuity reinsurance. JPY (¥)	Jun. 30, 2011 Level 1 Inputs USD ($)	Jun. 30, 2011 Level 1 Inputs USD ($)	Jun. 30, 2011 Level 2 Inputs USD ($)	Jun. 30, 2011 Level 2 Inputs USD ($)	Jun. 30, 2011 Level 3 Inputs USD ($)	Jun. 30, 2011 Level 3 Inputs USD ($)	Jun. 30, 2011 Fair Value USD ($)	Jun. 30, 2011 Fair Value USD ($)	Jun. 30, 2011 Fixed income/Interest rate USD ($)	Jun. 30, 2010 Fixed income/Interest rate USD ($)	Jun. 30, 2011 Fixed income/Interest rate USD ($)	Jun. 30, 2010 Fixed income/Interest rate USD ($)	Jun. 30, 2011 Foreign exchange USD ($)	Jun. 30, 2010 Foreign exchange USD ($)	Jun. 30, 2011 Foreign exchange USD ($)	Jun. 30, 2010 Foreign exchange USD ($)	Jun. 30, 2011 Equity USD ($)	Jun. 30, 2010 Equity USD ($)	Jun. 30, 2011 Equity USD ($)	Jun. 30, 2010 Equity USD ($)	Jun. 30, 2011 Other.
Variable annuity reinsurance
Total guarantee value																												$ 2,900,000,000	¥ 235,300,000,000	$ 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)																												83.00%	83.00%	82.00%	82.00%
Pre-tax operating results of WM Life Re
Fees, included in other revenues					8,000,000	7,200,000	15,900,000	14,500,000
Change in fair value of variable annuity liability, included in other revenues										(35,900,000)	(186,200,000)	16,400,000	(151,200,000)
Change in fair value of derivatives, included in other revenues	22,000,000	172,800,000	(43,500,000)	130,500,000	22,000,000	172,800,000	(43,500,000)	130,500,000																								2,800,000	(16,800,000)	12,500,000	(8,200,000)	6,700,000	(18,500,000)	22,000,000	(43,500,000)	(6,300,000)	19,200,000	(12,500,000)	23,400,000	17,100,000	74,500,000	(30,200,000)	68,500,000	11,200,000	79,100,000	(800,000)	38,600,000
Foreign exchange, included in other revenues					6,900,000	7,700,000	2,300,000	5,600,000
Other investment income and gains (losses)					(200,000)	(200,000)	(600,000)	(500,000)
Total revenues	571,100,000	689,600,000	1,119,100,000	1,503,300,000	800,000	1,300,000	(9,500,000)	(1,100,000)
Change in fair value of variable annuity death benefit liabilities, included in other expenses										(500,000)	(8,100,000)	(2,500,000)	(6,100,000)
Death benefit claims paid, included in other expenses					(700,000)	(400,000)	(1,700,000)	(800,000)
General and administrative expenses	(56,200,000)	(52,300,000)	(84,200,000)	(87,400,000)	(1,400,000)	(1,400,000)	(2,100,000)	(3,600,000)
Pre-tax income (loss) from continuing operations	34,400,000	4,000,000	(200,000)	(20,200,000)	(1,800,000)	(8,600,000)	(10,800,000)	(11,600,000)
Changes in variable annuity liabilities
Balance of liabilities, at the beginning of the period																										(554,900,000)	(610,200,000)
Realized and unrealized gains (losses)																										(36,400,000)	18,900,000
Balance of liabilities, at the end of the period																										(591,300,000)	(591,300,000)
Changes in derivative instruments
Balance of assets, at the beginning of the period			347,500,000																													7,300,000		54,800,000	72,200,000	226,000,000	275,300,000	288,100,000	347,500,000			43,900,000				225,300,000				78,300,000
Purchases																																					5,000,000		5,000,000
Realized and unrealized gains (losses)	22,000,000	172,800,000	(43,500,000)	130,500,000	22,000,000	172,800,000	(43,500,000)	130,500,000																								2,800,000	(16,800,000)	12,500,000	(8,200,000)	6,700,000	(18,500,000)	22,000,000	(43,500,000)	(6,300,000)	19,200,000	(12,500,000)	23,400,000	17,100,000	74,500,000	(30,200,000)	68,500,000	11,200,000	79,100,000	(800,000)	38,600,000
Sales/settlements																																(22,000,000)	4,900,000	(19,100,000)	(15,800,000)		(29,100,000)	(41,100,000)	(40,000,000)
Balance of assets, at the end of the period	269,000,000		269,000,000																							591,300,000	591,300,000					(11,900,000)	(11,900,000)	48,200,000	48,200,000	232,700,000	232,700,000	269,000,000	269,000,000	48,800,000		48,800,000		161,200,000		161,200,000		59,000,000		59,000,000
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	22,000,000	172,800,000	(43,500,000)	130,500,000	22,000,000	172,800,000	(43,500,000)	130,500,000																								2,800,000	(16,800,000)	12,500,000	(8,200,000)	6,700,000	(18,500,000)	22,000,000	(43,500,000)	(6,300,000)	19,200,000	(12,500,000)	23,400,000	17,100,000	74,500,000	(30,200,000)	68,500,000	11,200,000	79,100,000	(800,000)	38,600,000
Carrying Value	269,000,000		269,000,000																							591,300,000	591,300,000					(11,900,000)	(11,900,000)	48,200,000	48,200,000	232,700,000	232,700,000	269,000,000	269,000,000	48,800,000		48,800,000		161,200,000		161,200,000		59,000,000		59,000,000
Credit risk on derivative instruments
OTC derivative instruments					284,200,000		284,200,000		351,500,000
Collateral held					(52,600,000)		(52,600,000)		(101,000,000)							(1,000,000)	(48,600,000)	(51,600,000)	(52,400,000)
Collateral provided					35,400,000		35,400,000		25,300,000
Net exposure to credit losses on fair value of OTC instruments					267,000,000		267,000,000		275,800,000											73,500,000	73,400,000	50,100,000	25,900,000	9,800,000	34,300,000
Number of creditworthiness ratings	21		21
Percentage of the uncollateralized amount due under WM Life Re's derivative contracts for AA creditworthiness rating (as a percent)																																																				17.00%
Percentage of the uncollateralized amount due under WM Life Re's derivative contracts for A+ creditworthiness rating (as a percent)																																																				27.00%
Percentage of the uncollateralized amount due under WM Life Re's derivative contracts for BBB+ creditworthiness rating (as a percent)																																																				56.00%
Additional collateral					370,500,000		370,500,000		326,000,000					345,900,000	291,100,000	11,400,000	3,300,000	13,200,000	31,600,000
Adjustments for counterparty credit risk					$ (3,300,000)		$ (3,300,000)		$ (4,000,000)