Long-Term Debt - Schedule of Long Term Debt (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Debt Instrument [Line Items]
Long-term debt	$ 10,042	$ 9,699
Long-term Debt and Capital Lease Obligations	769	788
Increase (decrease) in carrying value of long-term debt	76	35
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
3.70% notes due in 2023(1)
Debt Instrument [Line Items]
Long-term debt	1,043	974
Debt Instrument, Interest Rate, Stated Percentage	3.70%
2.875% notes due 2016
Debt Instrument [Line Items]
Long-term debt	1,005	1,010
Debt Instrument, Interest Rate, Stated Percentage	2.875%
3.30% notes due 2024(1)
Debt Instrument [Line Items]
Long-term debt	999	0
3.10% subordinated notes due 2023(1)
Debt Instrument [Line Items]
Long-term debt	983	918
Debt Instrument, Interest Rate, Stated Percentage	3.10%
4.375% notes due 2021
Debt Instrument [Line Items]
Long-term debt	730	727
Debt Instrument, Interest Rate, Stated Percentage	4.375%
4.956% junior subordinated debentures due 2018
Debt Instrument [Line Items]
Long-term debt	528	537
Debt Instrument, Interest Rate, Stated Percentage	4.956%
4.30% notes due 2014
Debt Instrument [Line Items]
Long-term debt	0	502
Debt Instrument, Interest Rate, Stated Percentage	4.30%
1.35% notes due 2018(1)
Debt Instrument [Line Items]
Long-term debt	492	487
Debt Instrument, Interest Rate, Stated Percentage	1.35%
5.375% notes due 2017
Debt Instrument [Line Items]
Long-term debt	450	450
Debt Instrument, Interest Rate, Stated Percentage	5.375%
Floating-rate notes due 2014
Debt Instrument [Line Items]
Long-term debt	0	250
7.35% notes due 2026
Debt Instrument [Line Items]
Long-term debt	150	150
Debt Instrument, Interest Rate, Stated Percentage	7.35%
Floating-rate extendible notes due 2016
Debt Instrument [Line Items]
Long-term debt	900	900
5.25% subordinated notes due 2018
Debt Instrument [Line Items]
Long-term debt	433	442
Debt Instrument, Interest Rate, Stated Percentage	5.25%
5.30% subordinated notes due 2016
Debt Instrument [Line Items]
Long-term debt	405	409
Debt Instrument, Interest Rate, Stated Percentage	5.30%
Floating-rate subordinated notes due 2015
Debt Instrument [Line Items]
Long-term debt	200	200
Fair Value Hedges
Debt Instrument [Line Items]
Increase (decrease) in carrying value of long-term debt	$ 76	$ (35)