Regulatory Capital - U.S. Basel III Regulatory Requirements (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Actual Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 3,008,318	$ 2,896,091
Tier 1 Capital (to Risk-Weighted Assets)	3,008,318	2,896,091
Total Capital (to Risk-Weighted Assets)	3,324,527	3,196,279
Tier 1 Capital (to Average Assets)	$ 3,008,318	$ 2,896,091
Actual Ratio
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	11.90%	12.10%
Tier 1 Capital (to Risk-Weighted Assets)	11.90%	12.10%
Total Capital (to Risk-Weighted Assets)	13.20%	13.30%
Tier 1 Capital (to Average Assets)	10.60%	11.10%
Advanced Approach
U.S. Basel III Regulatory Requirements, Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 1,765,971	$ 1,528,209
Tier 1 Capital (to Risk-Weighted Assets)	2,144,394	1,887,787
Total Capital (to Risk-Weighted Assets)	2,648,957	2,367,226
Tier 1 Capital (to Average Assets)	$ 1,133,551	$ 1,039,226
U.S. Basel III Regulatory Requirements, Ratio
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	7.00%	6.375%
Tier 1 Capital (to Risk-Weighted Assets)	8.50%	7.875%
Total Capital (to Risk-Weighted Assets)	10.50%	9.875%
Tier 1 Capital (to Average Assets)	4.00%	4.00%