Regulatory Capital - U.S. Basel III Regulatory Requirements (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Actual Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 3,123,262	$ 2,896,091
Tier 1 Capital (to Risk-Weighted Assets)	3,123,262	2,896,091
Total Capital (to Risk-Weighted Assets)	3,462,407	3,196,279
Tier 1 Capital (to Average Assets)	$ 3,123,262	$ 2,896,091
Actual Ratio
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	11.50%	12.10%
Tier 1 Capital (to Risk-Weighted Assets)	11.50%	12.10%
Total Capital (to Risk-Weighted Assets)	12.80%	13.30%
Tier 1 Capital (to Average Assets)	10.30%	11.10%
Advanced Approach
U.S. Basel III Regulatory Requirements, Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 1,893,808	$ 1,528,209
Tier 1 Capital (to Risk-Weighted Assets)	2,299,624	1,887,787
Total Capital (to Risk-Weighted Assets)	2,840,712	2,367,226
Tier 1 Capital (to Average Assets)	$ 1,209,790	$ 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%