Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Available for Sale - Amortized Cost
ONE YEAR OR LESS	$ 6,255.1
ONE TO FIVE YEARS	15,054.3
FIVE TO TEN YEARS	5,478.8
OVER TEN YEARS	971.8
AMORTIZED COST	27,760.0	$ 37,948.5
Available for Sale - Fair Value
ONE YEAR OR LESS	6,151.0
ONE YEAR OR LESS	14,372.3
FIVE TO TEN YEARS	5,250.9
OVER TEN YEARS	925.7
Total	26,699.9	38,010.5
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	4,400.8
ONE TO FIVE YEARS	12,320.2
FIVE TO TEN YEARS	5,773.7
FIVE TO TEN YEARS	2,541.4
Amortized Cost	25,036.1	23,564.5
Held to Maturity - Fair Value
Fair value, one year or less	4,278.0
Fair value, one to five years	11,274.5
Fair value, five to ten years	5,172.2
Fair value, over ten years	2,154.6
FAIR VALUE	22,879.3	23,315.4
U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	1,576.6
ONE TO FIVE YEARS	1,261.1
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
AMORTIZED COST	2,837.7	2,406.2
Available for Sale - Fair Value
ONE YEAR OR LESS	1,574.5
ONE YEAR OR LESS	1,172.9
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Total	2,747.4	2,426.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	50.0
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
FIVE TO TEN YEARS	0.0
Amortized Cost	50.0	47.0
Held to Maturity - Fair Value
Fair value, one year or less	50.0
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	50.0	47.0
Obligations of States and Political Subdivisions
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	105.5
FIVE TO TEN YEARS	675.4
OVER TEN YEARS	36.9
AMORTIZED COST	817.8	3,841.0
Available for Sale - Fair Value
ONE YEAR OR LESS	0.0
ONE YEAR OR LESS	105.5
FIVE TO TEN YEARS	646.5
OVER TEN YEARS	35.6
Total	787.6	3,876.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	36.4
ONE TO FIVE YEARS	753.0
FIVE TO TEN YEARS	1,325.5
FIVE TO TEN YEARS	450.4
Amortized Cost	2,565.3	0.8
Held to Maturity - Fair Value
Fair value, one year or less	36.0
Fair value, one to five years	725.8
Fair value, five to ten years	1,242.3
Fair value, over ten years	411.4
FAIR VALUE	2,415.5	0.8
Government Sponsored Agency
Available for Sale - Amortized Cost
ONE YEAR OR LESS	2,452.0
ONE TO FIVE YEARS	5,602.6
FIVE TO TEN YEARS	3,060.2
OVER TEN YEARS	777.7
AMORTIZED COST	11,892.5	18,092.1
Available for Sale - Fair Value
ONE YEAR OR LESS	2,404.0
ONE YEAR OR LESS	5,441.7
FIVE TO TEN YEARS	2,962.5
OVER TEN YEARS	737.0
Total	11,545.2	18,075.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	879.8
ONE TO FIVE YEARS	2,957.6
FIVE TO TEN YEARS	3,629.7
FIVE TO TEN YEARS	1,940.6
Amortized Cost	9,407.7	5,927.6
Held to Maturity - Fair Value
Fair value, one year or less	775.0
Fair value, one to five years	2,624.9
Fair value, five to ten years	3,232.7
Fair value, over ten years	1,699.1
FAIR VALUE	8,331.7	5,822.6
Non-U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	101.3
ONE TO FIVE YEARS	286.3
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
AMORTIZED COST	387.6	383.4
Available for Sale - Fair Value
ONE YEAR OR LESS	101.1
ONE YEAR OR LESS	258.9
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Total	360.0	374.0
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	1,742.3
ONE TO FIVE YEARS	1,344.7
FIVE TO TEN YEARS	147.0
FIVE TO TEN YEARS	0.0
Amortized Cost	3,234.0
Held to Maturity - Fair Value
Fair value, one year or less	1,741.8
Fair value, one to five years	1,233.0
Fair value, five to ten years	125.5
Fair value, over ten years	0.0
FAIR VALUE	3,100.3
Corporate Debt
Available for Sale - Amortized Cost
ONE YEAR OR LESS	555.8
ONE TO FIVE YEARS	1,199.3
FIVE TO TEN YEARS	18.3
OVER TEN YEARS	0.9
AMORTIZED COST	1,774.3	2,319.8
Available for Sale - Fair Value
ONE YEAR OR LESS	551.8
ONE YEAR OR LESS	1,180.3
FIVE TO TEN YEARS	14.8
OVER TEN YEARS	0.7
Total	1,747.6	2,341.7
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	91.8
ONE TO FIVE YEARS	606.4
FIVE TO TEN YEARS	15.1
FIVE TO TEN YEARS	0.0
Amortized Cost	713.3	901.8
Held to Maturity - Fair Value
Fair value, one year or less	90.9
Fair value, one to five years	565.0
Fair value, five to ten years	12.0
Fair value, over ten years	0.0
FAIR VALUE	667.9	897.8
Covered Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	159.5
ONE TO FIVE YEARS	243.6
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
AMORTIZED COST	403.1	502.6
Available for Sale - Fair Value
ONE YEAR OR LESS	159.2
ONE YEAR OR LESS	229.5
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Total	388.7	505.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	410.5
ONE TO FIVE YEARS	1,699.8
FIVE TO TEN YEARS	420.0
FIVE TO TEN YEARS	0.0
Amortized Cost	2,530.3	2,942.4
Held to Maturity - Fair Value
Fair value, one year or less	408.6
Fair value, one to five years	1,607.6
Fair value, five to ten years	355.7
Fair value, over ten years	0.0
FAIR VALUE	2,371.9	2,941.1
Certificates of Deposit
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	35.9
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
FIVE TO TEN YEARS	0.0
Amortized Cost	35.9	674.7
Held to Maturity - Fair Value
Fair value, one year or less	35.9
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	35.9	674.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	498.9
ONE TO FIVE YEARS	1,923.7
FIVE TO TEN YEARS	223.2
OVER TEN YEARS	0.0
AMORTIZED COST	2,645.8	3,052.4
Available for Sale - Fair Value
ONE YEAR OR LESS	494.3
ONE YEAR OR LESS	1,802.7
FIVE TO TEN YEARS	182.4
OVER TEN YEARS	0.0
Total	2,479.4	3,045.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	1,019.0
ONE TO FIVE YEARS	4,554.6
FIVE TO TEN YEARS	129.7
FIVE TO TEN YEARS	0.0
Amortized Cost	5,703.3	6,098.0
Held to Maturity - Fair Value
Fair value, one year or less	1,006.8
Fair value, one to five years	4,154.1
Fair value, five to ten years	107.3
Fair value, over ten years	0.0
FAIR VALUE	5,268.2	6,032.3
Other Asset-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	893.7
ONE TO FIVE YEARS	3,244.1
FIVE TO TEN YEARS	1,250.2
OVER TEN YEARS	156.3
AMORTIZED COST	5,544.3	5,962.0
Available for Sale - Fair Value
ONE YEAR OR LESS	848.6
ONE YEAR OR LESS	3,035.5
FIVE TO TEN YEARS	1,219.7
OVER TEN YEARS	152.4
Total	5,256.2	5,941.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	88.6
ONE TO FIVE YEARS	102.9
FIVE TO TEN YEARS	72.2
FIVE TO TEN YEARS	0.0
Amortized Cost	263.7	682.6
Held to Maturity - Fair Value
Fair value, one year or less	88.4
Fair value, one to five years	102.4
Fair value, five to ten years	71.9
Fair value, over ten years	0.0
FAIR VALUE	262.7	683.6
Other
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	46.5
ONE TO FIVE YEARS	301.2
FIVE TO TEN YEARS	34.5
FIVE TO TEN YEARS	150.4
Amortized Cost	532.6	516.3
Held to Maturity - Fair Value
Fair value, one year or less	44.6
Fair value, one to five years	261.7
Fair value, five to ten years	24.8
Fair value, over ten years	44.1
FAIR VALUE	375.2	448.1
Commercial Mortgage-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	17.3
ONE TO FIVE YEARS	1,188.1
FIVE TO TEN YEARS	251.5
OVER TEN YEARS	0.0
AMORTIZED COST	1,456.9	1,389.0
Available for Sale - Fair Value
ONE YEAR OR LESS	17.5
ONE YEAR OR LESS	1,145.3
FIVE TO TEN YEARS	225.0
OVER TEN YEARS	0.0
Total	$ 1,387.8	$ 1,424.7