Regulatory Capital - U.S. Basel III Regulatory Requirements (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Actual Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 3,112,763	$ 3,264,309
Tier 1 Capital (to Risk-Weighted Assets)	3,112,763	3,264,309
Total Capital (to Risk-Weighted Assets)	3,428,154	3,600,668
Tier 1 Capital (to Average Assets)	$ 3,112,763	$ 3,264,309
Actual Ratio
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	12.40%	12.20%
Tier 1 Capital (to Risk-Weighted Assets)	12.40%	12.20%
Total Capital (to Risk-Weighted Assets)	13.70%	13.40%
Tier 1 Capital (to Average Assets)	9.40%	10.20%
Advanced Approach
U.S. Basel III Regulatory Requirements, Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 1,757,168	$ 1,876,050
Tier 1 Capital (to Risk-Weighted Assets)	2,133,704	2,278,060
Total Capital (to Risk-Weighted Assets)	2,635,752	2,814,074
Tier 1 Capital (to Average Assets)	$ 1,326,107	$ 1,284,642
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)	8.50%	8.50%
Total Capital (to Risk-Weighted Assets)	10.50%	10.50%
Tier 1 Capital (to Average Assets)	4.00%	4.00%