Long-Term Debt - Schedule of Long Term Debt (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Aug. 31, 2015
Debt Instrument [Line Items]
Long-term debt	$ 11,534	$ 10,042
Fair Value Hedges
Debt Instrument [Line Items]
Increase (decrease) in carrying value of long-term debt	105	76
Floating-rate notes due 2020
Debt Instrument [Line Items]
Long-term debt	500	0
Subordinated note | Floating-rate subordinated notes due to State Street Capital Trust IV in 2037
Debt Instrument [Line Items]
Long-term debt	800	800
Subordinated note | Floating-rate subordinated notes due to State Street Capital Trust I in 2028
Debt Instrument [Line Items]
Long-term debt	155	155
Subordinated note | 3.10% subordinated notes due 2023
Debt Instrument [Line Items]
Long-term debt	$ 997	983
Interest rate on debt	3.10%
Subordinated note | Floating-rate extendible notes due 2016
Debt Instrument [Line Items]
Long-term debt	$ 0	900
Subordinated note | 5.25% subordinated notes due 2018
Debt Instrument [Line Items]
Long-term debt	$ 424	433
Interest rate on debt	5.25%
Subordinated note | 5.30% subordinated notes due 2016
Debt Instrument [Line Items]
Long-term debt	$ 400	405
Interest rate on debt	5.30%
Subordinated note | Floating-rate subordinated notes due 2015
Debt Instrument [Line Items]
Long-term debt	$ 0	200
Senior notes | 3.55% notes due 2025
Debt Instrument [Line Items]
Long-term debt	$ 1,307	0
Interest rate on debt	3.55%		3.55%
Senior notes | 2.55% notes due 2020
Debt Instrument [Line Items]
Long-term debt	$ 1,199	0
Interest rate on debt	2.55%		2.55%
Senior notes | 3.70% notes due in 2023
Debt Instrument [Line Items]
Long-term debt	$ 1,050	1,043
Interest rate on debt	3.70%
Senior notes | 3.30% notes due 2024
Debt Instrument [Line Items]
Long-term debt	$ 1,013	999
Interest rate on debt	3.30%
Senior notes | 2.875% notes due 2016
Debt Instrument [Line Items]
Long-term debt	$ 1,001	1,005
Interest rate on debt	2.875%
Senior notes | 4.375% notes due 2021
Debt Instrument [Line Items]
Long-term debt	$ 740	730
Interest rate on debt	4.375%
Senior notes | 1.35% notes due 2018
Debt Instrument [Line Items]
Long-term debt	$ 496	492
Interest rate on debt	1.35%
Senior notes | 5.375% notes due 2017
Debt Instrument [Line Items]
Long-term debt	$ 449	450
Interest rate on debt	5.375%
Senior notes | 7.35% notes due 2026
Debt Instrument [Line Items]
Long-term debt	$ 150	150
Interest rate on debt	7.35%
Junior Subordinated Debt | 4.956% junior subordinated debentures due 2018
Debt Instrument [Line Items]
Long-term debt	$ 519	528
Interest rate on debt	4.956%
Capital Lease Obligations
Debt Instrument [Line Items]
Long-term capital leases	$ 334	$ 769