Regulation and Capital Adequacy - Risk-based Capital Ratios (Detail) $ in Millions	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)
Standardized Capital Rules [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 capital	$ 77,503	$ 74,850	$ 73,116
Tier 1 capital	88,566	85,440	83,702
Tier 2 capital	16,018	14,925	14,926
Total capital	104,584	100,365
RWAs	$ 534,557	$ 563,575	547,910
CET1 capital ratio	0.145	0.133
Tier 1 capital ratio	0.166	0.152
Total capital ratio	0.196	0.178
Advanced Capital [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 capital	$ 77,503	$ 74,850	73,116
Tier 1 capital	88,566	85,440	83,702
Tier 2 capital	14,067	13,473	13,743
Total capital	102,633	98,913
RWAs	$ 599,626	$ 544,653	$ 558,111
CET1 capital ratio	0.129	0.137
Tier 1 capital ratio	0.148	0.157
Total capital ratio	0.171	0.182
GS Bank USA [Member] | Standardized Capital Rules [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 capital	$ 30,441	$ 29,176
Tier 1 capital	30,441	29,176
Tier 2 capital	6,235	5,293
Total capital	36,676	34,469
RWAs	$ 247,064	$ 258,541
CET1 capital ratio	0.123	0.113
Tier 1 capital ratio	0.123	0.113
Total capital ratio	0.148	0.133
GS Bank USA [Member] | Advanced Capital [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
CET1 capital	$ 30,441	$ 29,176
Tier 1 capital	30,441	29,176
Tier 2 capital	4,852	4,486
Total capital	35,293	33,662
RWAs	$ 160,261	$ 135,596
CET1 capital ratio	0.190	0.215
Tier 1 capital ratio	0.190	0.215
Total capital ratio	0.220	0.248