Regulatory Capital - Narrative (Details)	Sep. 30, 2017	Jan. 01, 2017	Dec. 31, 2016	Jan. 01, 2015
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 capital (to risk weighted assets), for capital adequacy purposes ratio	7.25%	7.25%	6.625%	6.00%
Tier 1 capital (to risk weighted assets), to be well capitalized under prompt corrective action provisions ratio				8.00%
Capital conservation buffer, excess of minimum capital ratio				2.50%
Capital conservation buffer to risk weighted assets, year one	0.625%
Capital conservation buffer to risk weighted assets, year two	1.25%
Capital conservation buffer to risk weighted assets, year three	1.875%
Capital conservation buffer to risk weighted assets, year four and thereafter	2.50%
Common equity Tier 1 (to risk weighted assets), for capital adequacy purposes ratio	5.75%	5.75%	5.125%
Total capital (to risk weighted assets), for capital adequacy purposes ratio	9.25%	9.25%	8.625%
Customers Bank
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Tier 1 capital (to risk weighted assets), for capital adequacy purposes ratio	7.25%	7.25%	6.625%
Tier 1 capital (to risk weighted assets), to be well capitalized under prompt corrective action provisions ratio	8.00%		8.00%
Common equity Tier 1 (to risk weighted assets), for capital adequacy purposes ratio	5.75%	5.75%	5.125%
Total capital (to risk weighted assets), for capital adequacy purposes ratio	9.25%	9.25%	8.625%