Shareholders' Equity (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2011	Mar. 31, 2011	Jun. 30, 2011	Jun. 30, 2010	Dec. 31, 2010	Dec. 31, 2009
Non-cumulative perpetual preferred stock, shares	5,001	5,001	5,001		5,001
Non-cumulative perpetual preferred stock	$ 500	$ 500	$ 500
Series A, liquidation preference per share		$ 100,000
Common stock purchase program, authorized amount		675
Common shares available for purchase					13,250,000
Treasury stock purchased	4,900,000
Average historical cost per share	$ 46.18
Realized (losses) gains from sales of investment securities			66	195
Unrealized pre-tax gains (losses) included in other comprehensive income					76	131
Deferred taxes related to unrealized pre-tax gains					$ 30	$ 52
State Street Capital Trust III [Member ]
Subordinated borrowing, interest rate		6.001%
Junior subordinated debentures, due date		2042