Long-Term Debt (Long-Term Debt) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010
Debt Instrument [Line Items]
Long-term debt	$ 8,131		$ 8,550
Long-term capital leases	694		716
Increase in carrying value of long-term debt	140		81
Floating-Rate Subordinated Notes Due To State Street Capital Trust IV In 2037 [Member]
Debt Instrument [Line Items]
Long-term debt	800		800
Subordinated borrowing, due date	Jan. 01, 2037
Floating-Rate Subordinated Notes Due To State Street Capital Trust I In 2028 [Member]
Debt Instrument [Line Items]
Long-term debt	155		155
Subordinated borrowing, due date	Jan. 01, 2028
Subordinated Notes Due To State Street Capital Trust III In 2042 [Member]
Debt Instrument [Line Items]
Long-term debt			500
Subordinated borrowing, due date	Jan. 01, 2042
2.15% Notes Due 2012 [Member]
Debt Instrument [Line Items]
Long-term debt	1,500	[1]	1,499	[1]
Subordinated borrowing interest rate	2.15%
Subordinated borrowing, due date	Apr. 30, 2012
2.875% Notes Due 2016 [Member]
Debt Instrument [Line Items]
Long-term debt	999	[2]
Subordinated borrowing interest rate	2.875%
Subordinated borrowing, due date	Jan. 01, 2016
4.375% Notes Due 2021 [Member]
Debt Instrument [Line Items]
Long-term debt	757	[2]
Subordinated borrowing interest rate	4.375%
Subordinated borrowing, due date	Jan. 01, 2021
4.956% Junior Subordinated Debentures Due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	542
Subordinated borrowing interest rate	4.956%
Subordinated borrowing, due date	Mar. 15, 2018
4.30% Notes Due 2014 [Member]
Debt Instrument [Line Items]
Long-term debt	512		500
Subordinated borrowing interest rate	4.30%
Subordinated borrowing, due date	May 30, 2014
5.375% Notes Due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt	450		450
Subordinated borrowing interest rate	5.375%
Subordinated borrowing, due date	Apr. 30, 2017
Floating-Rate Notes Due 2012 [Member]
Debt Instrument [Line Items]
Long-term debt	250		268
Subordinated borrowing, due date	Apr. 30, 2012
Floating-Rate Notes Due 2014 [Member]
Debt Instrument [Line Items]
Long-term debt	250
Subordinated borrowing, due date	Jan. 01, 2014
7.35% Notes Due 2026 [Member]
Debt Instrument [Line Items]
Long-term debt	150		150
Subordinated borrowing interest rate	7.35%
Subordinated borrowing, due date	Jun. 15, 2026
5.25% Subordinated Notes Due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt	453	[2]	439	[2]
Subordinated borrowing interest rate	5.25%
Subordinated borrowing, due date	Jan. 01, 2018
5.30% Subordinated Notes Due 2016 [Member]
Debt Instrument [Line Items]
Long-term debt	419		423
Subordinated borrowing interest rate	5.30%
Subordinated borrowing, due date	Jan. 01, 2016
Floating Rate Subordinated Notes Due 2015 [Member]
Debt Instrument [Line Items]
Long-term debt	200		200
Subordinated borrowing, due date	Jan. 01, 2015
Floating-Rate Notes Due 2011 [Member]
Debt Instrument [Line Items]
Long-term debt			1,450	[1]
Subordinated borrowing, due date	Jan. 01, 2011
1.85% Notes Due 2011 [Member]
Debt Instrument [Line Items]
Long-term debt			1,000	[1]
Subordinated borrowing interest rate	1.85%
Subordinated borrowing, due date	Jan. 01, 2011
Fair Value Hedges [Member]
Debt Instrument [Line Items]
Increase in carrying value of long-term debt	$ 140		$ 81

[1] Notes are guaranteed by the FDIC under its Temporary Liquidity Guarantee Program, or TLGP.

[2] We have entered into interest-rate swap agreements, recorded as fair value hedges, to modify our interest expense on these subordinated notes from a fixed rate to a floating rate. As of December 31, 2011 and 2010, we recorded an increase of $140 million and $81 million, respectively, in the carrying value of long-term debt associated with fair value hedges. Refer to note 16 for additional information about derivatives.