Regulatory Capital - U.S. Basel III Regulatory Requirements (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Actual Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 3,230,078	$ 3,264,309
Tier 1 Capital (to Risk-Weighted Assets)	3,230,078	3,264,309
Total Capital (to Risk-Weighted Assets)	3,551,765	3,600,668
Tier 1 Capital (to Average Assets)	$ 3,230,078	$ 3,264,309
Actual Ratio
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	12.70%	12.20%
Tier 1 Capital (to Risk-Weighted Assets)	0.127	0.122
Total Capital (to Risk-Weighted Assets)	0.139	0.134
Tier 1 Capital (to Average Assets)	0.102	0.102
Advanced Approach
U.S. Basel III Regulatory Requirements, Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 1,785,181	$ 1,876,050
Tier 1 Capital (to Risk-Weighted Assets)	2,167,720	2,278,060
Total Capital (to Risk-Weighted Assets)	2,677,771	2,814,074
Tier 1 Capital (to Average Assets)	$ 1,261,080	$ 1,282,642
U.S. Basel III Regulatory Requirements, Ratio
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	7.00%	7.00%
Tier 1 Capital (to Risk-Weighted Assets)	0.085	0.085
Total Capital (to Risk-Weighted Assets)	0.105	0.105
Tier 1 Capital (to Average Assets)	0.040	0.040