Regulatory Capital - U.S. Basel III Regulatory Requirements (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Actual Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 3,255,466	$ 3,579,005
Tier 1 Capital (to Risk-Weighted Assets)	3,255,466	3,579,005
Total Capital (to Risk-Weighted Assets)	3,408,359	3,849,820
Tier 1 Capital (to Average Assets)	$ 3,255,466	$ 3,579,005
Actual Ratio
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	13.10%	14.00%
Tier 1 Capital (to Risk-Weighted Assets)	0.131	0.140
Total Capital (to Risk-Weighted Assets)	0.137	0.150
Tier 1 Capital (to Average Assets)	0.109	0.113
Advanced Approach
U.S. Basel III Regulatory Requirements, Amount
Common Equity Tier 1 Capital (to Risk-Weighted Assets)	$ 1,736,176	$ 1,794,780
Tier 1 Capital (to Risk-Weighted Assets)	2,108,214	2,179,375
Total Capital (to Risk-Weighted Assets)	2,604,265	2,692,169
Tier 1 Capital (to Average Assets)	$ 1,193,100	$ 1,264,424
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