Long-Term Debt (Long-Term Debt) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011
Debt Instrument [Line Items]
Long-term debt	$ 7,429		$ 8,131
Long-term capital leases	706		694
Increase in carrying value of long-term debt	174		140
Fair Value Hedges
Debt Instrument [Line Items]
Increase in carrying value of long-term debt	174		140
Floating-rate subordinated notes due to State Street Capital Trust IV in 2037
Debt Instrument [Line Items]
Long-term debt	800		800
Floating-rate subordinated notes due to State Street Capital Trust I in 2028
Debt Instrument [Line Items]
Long-term debt	155		155
2.15% notes due 2012
Debt Instrument [Line Items]
Long-term debt	0		1,500
2.875% notes due 2016(1)
Debt Instrument [Line Items]
Long-term debt	1,014	[1]	999	[1]
4.375% notes due 2021(1)
Debt Instrument [Line Items]
Long-term debt	780	[1]	757	[1]
4.956% junior subordinated debentures due 2018(1)
Debt Instrument [Line Items]
Long-term debt	550	[1]	542	[1]
4.30% notes due 2014
Debt Instrument [Line Items]
Long-term debt	507		512
5.375% notes due 2017
Debt Instrument [Line Items]
Long-term debt	450		450
Floating-rate notes due 2012
Debt Instrument [Line Items]
Long-term debt	0		250
Floating-rate notes due 2014
Debt Instrument [Line Items]
Long-term debt	250		250
7.35% notes due 2026
Debt Instrument [Line Items]
Long-term debt	150		150
Extendible notes due 2014
Debt Instrument [Line Items]
Long-term debt	1,000		0
5.25% subordinated notes due 2018(1)
Debt Instrument [Line Items]
Long-term debt	453	[1]	453	[1]
5.30% subordinated notes due 2016
Debt Instrument [Line Items]
Long-term debt	414		419
Floating-rate subordinated notes due 2015
Debt Instrument [Line Items]
Long-term debt	$ 200		$ 200

[1] We have entered into interest-rate swap agreements, recorded as fair value hedges, to modify our interest expense on these senior and subordinated notes from a fixed rate to a floating rate. As of December 31, 2012 and 2011, we recorded an increase of $174 million and $140 million, respectively, in the carrying value of long-term debt associated with fair value hedges. Refer to note 16 for additional information about derivatives.