Schedule II (BALANCE SHEETS - Parent Company Only) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011	Dec. 31, 2010		Dec. 31, 2009
Assets
Investments in subsidiaries and affiliates on equity basis
Short-term investments	2,228		2,301
Other investments	2,716		2,314
Cash	615	[1],[2]	614	772	[3],[4]	669	[3]
Due from subsidiaries and affiliates, net
Other assets	2,871		2,495
Total assets	92,545		87,321
Liabilities
Accounts payable, accrued expenses, and other liabilities	5,377		4,898
Short-term debt	1,401		1,251
Total liabilities	65,014		62,989
Stockholders' Equity Attributable to Parent [Abstract]
Common Shares	9,591		10,095
Common Shares in treasury	(159)		(327)
Additional paid-in capital	5,179		5,326
Retained earnings	10,033		7,327
Accumulated other comprehensive income	2,887		1,911
Total liabilities and shareholders' equity	92,545		87,321
Parent Company Only
Assets
Investments in subsidiaries and affiliates on equity basis	27,251		23,871
Short-term investments	1		1
Other investments	30		32
Total investments	27,282		23,904
Cash	103	[1],[2]	106	308	[4]	(1)	[3]
Due from subsidiaries and affiliates, net	204		498
Other assets	13		8
Total assets	27,602		24,516
Liabilities
Accounts payable, accrued expenses, and other liabilities	71		65
Dividends payable	0		119
Short-term debt
Total liabilities	71		184
Stockholders' Equity Attributable to Parent [Abstract]
Common Shares	9,591		10,095
Common Shares in treasury	(159)		(327)
Additional paid-in capital	5,179		5,326
Retained earnings	10,033		7,327
Accumulated other comprehensive income	2,887		1,911
Total shareholders' equity	27,531		24,332
Total liabilities and shareholders' equity	$ 27,602		$ 24,516

[1] ACE maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1f) for additional information. At December 31, 2012, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[2] ACE maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 2012, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[3] ACE maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 2010 and 2009, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.

[4] ACE maintains two notional multi-currency cash pools (Pools) with a third-party bank. Refer to Note 1 f) for additional information. At December 31, 2010, the cash balance of one or more entities was negative; however, the overall Pool balances were positive.