Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Available for Sale - Amortized Cost
Amortized cost, one year or less	$ 5,009.6
Amortized cost, one to five years	19,648.5
Amortized cost, five to ten years	11,748.3
Amortized cost, over ten years	1,542.1
AMORTIZED COST	37,948.5	$ 41,155.7
Available for Sale - Fair Value
Fair value, one year or less	5,028.9
Fair value, one to five years	19,718.1
Fair value, five to ten years	11,725.5
Fair value, over ten years	1,538.0
Total	38,010.5	42,022.0
Held to Maturity - Amortized Cost
Amortized cost, one year or less	8,597.5
Amortized cost, one to five years	10,740.6
Amortized cost, five to ten years	3,292.3
Amortized cost, over ten years	934.1
Amortized Cost	23,564.5	17,791.1
Held to Maturity - Fair Value
Fair value, one year or less	8,585.0
Fair value, one to five years	10,631.8
Fair value, five to ten years	3,235.4
Fair value, over ten years	863.2
FAIR VALUE	23,315.4	17,797.4
U.S. Government
Available for Sale - Amortized Cost
Amortized cost, one year or less	0.0
Amortized cost, one to five years	2,157.8
Amortized cost, five to ten years	248.4
Amortized cost, over ten years	0.0
AMORTIZED COST	2,406.2	2,728.8
Available for Sale - Fair Value
Fair value, one year or less	0.0
Fair value, one to five years	2,187.1
Fair value, five to ten years	239.0
Fair value, over ten years	0.0
Total	2,426.1	2,799.9
Held to Maturity - Amortized Cost
Amortized cost, one year or less	47.0
Amortized cost, one to five years	0.0
Amortized cost, five to ten years	0.0
Amortized cost, over ten years	0.0
Amortized Cost	47.0	90.0
Held to Maturity - Fair Value
Fair value, one year or less	47.0
Fair value, one to five years	0.0
Fair value, five to ten years	0.0
Fair value, over ten years	0.0
FAIR VALUE	47.0	90.0
Obligations of States and Political Subdivisions
Available for Sale - Amortized Cost
Amortized cost, one year or less	22.8
Amortized cost, one to five years	448.3
Amortized cost, five to ten years	3,239.7
Amortized cost, over ten years	130.2
AMORTIZED COST	3,841.0	2,927.8
Available for Sale - Fair Value
Fair value, one year or less	23.0
Fair value, one to five years	462.1
Fair value, five to ten years	3,262.6
Fair value, over ten years	128.4
Total	3,876.1	3,083.6
Held to Maturity - Amortized Cost
Amortized cost, one year or less	0.8
Amortized cost, one to five years	0.0
Amortized cost, five to ten years	0.0
Amortized cost, over ten years	0.0
Amortized Cost	0.8	2.1
Held to Maturity - Fair Value
Fair value, one year or less	0.8
Fair value, one to five years	0.0
Fair value, five to ten years	0.0
Fair value, over ten years	0.0
FAIR VALUE	0.8	2.2
Government Sponsored Agency
Available for Sale - Amortized Cost
Amortized cost, one year or less	2,706.1
Amortized cost, one to five years	8,112.2
Amortized cost, five to ten years	6,084.0
Amortized cost, over ten years	1,189.8
AMORTIZED COST	18,092.1	24,595.1
Available for Sale - Fair Value
Fair value, one year or less	2,713.2
Fair value, one to five years	8,121.1
Fair value, five to ten years	6,053.4
Fair value, over ten years	1,187.9
Total	18,075.6	24,956.7
Held to Maturity - Amortized Cost
Amortized cost, one year or less	1,161.5
Amortized cost, one to five years	2,101.4
Amortized cost, five to ten years	1,848.8
Amortized cost, over ten years	815.9
Amortized Cost	5,927.6	3.0
Held to Maturity - Fair Value
Fair value, one year or less	1,143.6
Fair value, one to five years	2,064.6
Fair value, five to ten years	1,815.0
Fair value, over ten years	799.4
FAIR VALUE	5,822.6	3.3
Non-U.S. Government
Available for Sale - Amortized Cost
Amortized cost, one year or less	72.7
Amortized cost, one to five years	228.4
Amortized cost, five to ten years	82.3
Amortized cost, over ten years	0.0
AMORTIZED COST	383.4
Available for Sale - Fair Value
Fair value, one year or less	72.7
Fair value, one to five years	223.1
Fair value, five to ten years	78.2
Fair value, over ten years	0.0
Total	374.0
Held to Maturity - Amortized Cost
Amortized cost, one year or less	4,502.7
Amortized cost, one to five years	1,109.2
Amortized cost, five to ten years	161.4
Amortized cost, over ten years	0.0
Amortized Cost	5,773.3	8,336.6
Held to Maturity - Fair Value
Fair value, one year or less	4,502.6
Fair value, one to five years	1,103.9
Fair value, five to ten years	160.9
Fair value, over ten years	0.0
FAIR VALUE	5,767.4	8,343.7
Corporate Debt
Available for Sale - Amortized Cost
Amortized cost, one year or less	404.4
Amortized cost, one to five years	1,892.6
Amortized cost, five to ten years	18.1
Amortized cost, over ten years	4.7
AMORTIZED COST	2,319.8	2,459.9
Available for Sale - Fair Value
Fair value, one year or less	408.0
Fair value, one to five years	1,911.6
Fair value, five to ten years	17.5
Fair value, over ten years	4.6
Total	2,341.7	2,539.6
Held to Maturity - Amortized Cost
Amortized cost, one year or less	177.4
Amortized cost, one to five years	708.3
Amortized cost, five to ten years	16.1
Amortized cost, over ten years	0.0
Amortized Cost	901.8	588.0
Held to Maturity - Fair Value
Fair value, one year or less	178.8
Fair value, one to five years	703.4
Fair value, five to ten years	15.6
Fair value, over ten years	0.0
FAIR VALUE	897.8	594.4
Covered Bonds
Available for Sale - Amortized Cost
Amortized cost, one year or less	141.5
Amortized cost, one to five years	361.1
Amortized cost, five to ten years	0.0
Amortized cost, over ten years	0.0
AMORTIZED COST	502.6	543.1
Available for Sale - Fair Value
Fair value, one year or less	142.1
Fair value, one to five years	363.5
Fair value, five to ten years	0.0
Fair value, over ten years	0.0
Total	505.6	553.1
Held to Maturity - Amortized Cost
Amortized cost, one year or less	650.1
Amortized cost, one to five years	1,684.0
Amortized cost, five to ten years	608.3
Amortized cost, over ten years	0.0
Amortized Cost	2,942.4	3,184.6
Held to Maturity - Fair Value
Fair value, one year or less	651.3
Fair value, one to five years	1,688.0
Fair value, five to ten years	601.8
Fair value, over ten years	0.0
FAIR VALUE	2,941.1	3,208.9
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Amortized Cost
Amortized cost, one year or less	760.6
Amortized cost, one to five years	1,926.8
Amortized cost, five to ten years	365.0
Amortized cost, over ten years	0.0
AMORTIZED COST	3,052.4	2,281.7
Available for Sale - Fair Value
Fair value, one year or less	765.7
Fair value, one to five years	1,926.1
Fair value, five to ten years	353.3
Fair value, over ten years	0.0
Total	3,045.1	2,345.8
Held to Maturity - Amortized Cost
Amortized cost, one year or less	1,086.9
Amortized cost, one to five years	4,507.7
Amortized cost, five to ten years	503.4
Amortized cost, over ten years	0.0
Amortized Cost	6,098.0	3,648.0
Held to Maturity - Fair Value
Fair value, one year or less	1,091.5
Fair value, one to five years	4,451.4
Fair value, five to ten years	489.4
Fair value, over ten years	0.0
FAIR VALUE	6,032.3	3,690.6
Other Asset-Backed
Available for Sale - Amortized Cost
Amortized cost, one year or less	894.0
Amortized cost, one to five years	3,559.0
Amortized cost, five to ten years	1,291.6
Amortized cost, over ten years	217.4
AMORTIZED COST	5,962.0	3,953.5
Available for Sale - Fair Value
Fair value, one year or less	896.8
Fair value, one to five years	3,541.4
Fair value, five to ten years	1,286.3
Fair value, over ten years	217.1
Total	5,941.6	3,997.5
Held to Maturity - Amortized Cost
Amortized cost, one year or less	190.4
Amortized cost, one to five years	398.0
Amortized cost, five to ten years	94.2
Amortized cost, over ten years	0.0
Amortized Cost	682.6	677.0
Held to Maturity - Fair Value
Fair value, one year or less	190.6
Fair value, one to five years	398.7
Fair value, five to ten years	94.3
Fair value, over ten years	0.0
FAIR VALUE	683.6	677.9
Commercial Mortgage-Backed
Available for Sale - Amortized Cost
Amortized cost, one year or less	7.5
Amortized cost, one to five years	962.3
Amortized cost, five to ten years	419.2
Amortized cost, over ten years	0.0
AMORTIZED COST	1,389.0	952.2
Available for Sale - Fair Value
Fair value, one year or less	7.4
Fair value, one to five years	982.1
Fair value, five to ten years	435.2
Fair value, over ten years	0.0
Total	1,424.7	1,031.8
Certificates of Deposit
Held to Maturity - Amortized Cost
Amortized cost, one year or less	674.7
Amortized cost, one to five years	0.0
Amortized cost, five to ten years	0.0
Amortized cost, over ten years	0.0
Amortized Cost	674.7	807.2
Held to Maturity - Fair Value
Fair value, one year or less	674.7
Fair value, one to five years	0.0
Fair value, five to ten years	0.0
Fair value, over ten years	0.0
FAIR VALUE	674.7	807.2
Other
Held to Maturity - Amortized Cost
Amortized cost, one year or less	106.0
Amortized cost, one to five years	232.0
Amortized cost, five to ten years	60.1
Amortized cost, over ten years	118.2
Amortized Cost	516.3	454.6
Held to Maturity - Fair Value
Fair value, one year or less	104.1
Fair value, one to five years	221.8
Fair value, five to ten years	58.4
Fair value, over ten years	63.8
FAIR VALUE	$ 448.1	$ 379.2