Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Jun. 30, 2023	Dec. 31, 2022
Available for Sale - Amortized Cost
ONE YEAR OR LESS	$ 5,584.6
ONE TO FIVE YEARS	13,750.9
FIVE TO TEN YEARS	4,971.3
OVER TEN YEARS	881.6
AMORTIZED COST	25,188.4	$ 27,760.0
Available for Sale - Fair Value
ONE YEAR OR LESS	5,472.5
ONE TO FIVE YEARS	13,153.9
FIVE TO TEN YEARS	4,798.5
OVER TEN YEARS	839.5
FAIR VALUE	24,264.4	26,699.9
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	5,329.1
ONE TO FIVE YEARS	12,821.2
FIVE TO TEN YEARS	5,433.5
OVER TEN YEARS	2,422.5
Amortized Cost	26,006.3	25,036.1
Held to Maturity - Fair Value
ONE YEAR OR LESS	5,192.9
ONE TO FIVE YEARS	11,629.9
FIVE TO TEN YEARS	4,895.1
OVER TEN YEARS	2,041.3
Fair Value	23,759.2	22,879.3
U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	1,094.4
ONE TO FIVE YEARS	1,847.9
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
AMORTIZED COST	2,942.3	2,837.7
Available for Sale - Fair Value
ONE YEAR OR LESS	1,092.7
ONE TO FIVE YEARS	1,751.2
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
FAIR VALUE	2,843.9	2,747.4
Held to Maturity - Amortized Cost
Amortized Cost		50.0
Held to Maturity - Fair Value
Fair Value		50.0
Obligations of States and Political Subdivisions
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	45.1
FIVE TO TEN YEARS	246.2
OVER TEN YEARS	18.9
AMORTIZED COST	310.2	817.8
Available for Sale - Fair Value
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	41.6
FIVE TO TEN YEARS	229.5
OVER TEN YEARS	18.1
FAIR VALUE	289.2	787.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	45.0
ONE TO FIVE YEARS	909.3
FIVE TO TEN YEARS	1,218.2
OVER TEN YEARS	400.5
Amortized Cost	2,573.0	2,565.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	44.4
ONE TO FIVE YEARS	875.0
FIVE TO TEN YEARS	1,163.9
OVER TEN YEARS	381.4
Fair Value	2,464.7	2,415.5
Government Sponsored Agency
Available for Sale - Amortized Cost
ONE YEAR OR LESS	2,278.8
ONE TO FIVE YEARS	5,336.1
FIVE TO TEN YEARS	3,282.9
OVER TEN YEARS	758.6
AMORTIZED COST	11,656.4	11,892.5
Available for Sale - Fair Value
ONE YEAR OR LESS	2,236.5
ONE TO FIVE YEARS	5,196.1
FIVE TO TEN YEARS	3,197.8
OVER TEN YEARS	718.6
FAIR VALUE	11,349.0	11,545.2
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	876.5
ONE TO FIVE YEARS	3,058.1
FIVE TO TEN YEARS	3,592.4
OVER TEN YEARS	1,827.2
Amortized Cost	9,354.2	9,407.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	765.3
ONE TO FIVE YEARS	2,692.9
FIVE TO TEN YEARS	3,180.0
OVER TEN YEARS	1,578.8
Fair Value	8,217.0	8,331.7
Non-U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	277.8
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
AMORTIZED COST	277.8	387.6
Available for Sale - Fair Value
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	251.5
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
FAIR VALUE	251.5	360.0
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	2,555.9
ONE TO FIVE YEARS	1,398.0
FIVE TO TEN YEARS	33.4
OVER TEN YEARS	0.0
Amortized Cost	3,987.3	3,234.0
Held to Maturity - Fair Value
ONE YEAR OR LESS	2,550.7
ONE TO FIVE YEARS	1,263.3
FIVE TO TEN YEARS	27.9
OVER TEN YEARS	0.0
Fair Value	3,841.9	3,100.3
Corporate Debt
Available for Sale - Amortized Cost
ONE YEAR OR LESS	198.5
ONE TO FIVE YEARS	263.8
FIVE TO TEN YEARS	17.4
OVER TEN YEARS	0.0
AMORTIZED COST	479.7	1,774.3
Available for Sale - Fair Value
ONE YEAR OR LESS	197.0
ONE TO FIVE YEARS	249.1
FIVE TO TEN YEARS	14.8
OVER TEN YEARS	0.0
FAIR VALUE	460.9	1,747.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	107.0
ONE TO FIVE YEARS	547.5
FIVE TO TEN YEARS	15.4
OVER TEN YEARS	0.0
Amortized Cost	669.9	713.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	104.3
ONE TO FIVE YEARS	506.5
FIVE TO TEN YEARS	12.4
OVER TEN YEARS	0.0
Fair Value	623.2	667.9
Covered Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	134.1
ONE TO FIVE YEARS	219.5
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
AMORTIZED COST	353.6	403.1
Available for Sale - Fair Value
ONE YEAR OR LESS	133.6
ONE TO FIVE YEARS	207.4
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
FAIR VALUE	341.0	388.7
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	224.0
ONE TO FIVE YEARS	1,741.4
FIVE TO TEN YEARS	313.3
OVER TEN YEARS	0.0
Amortized Cost	2,278.7	2,530.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	219.1
ONE TO FIVE YEARS	1,638.8
FIVE TO TEN YEARS	269.8
OVER TEN YEARS	0.0
Fair Value	2,127.7	2,371.9
Certificates of Deposit
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	588.2
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	588.2	35.9
Held to Maturity - Fair Value
ONE YEAR OR LESS	588.4
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	588.4	35.9
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	649.2
ONE TO FIVE YEARS	2,256.2
FIVE TO TEN YEARS	162.6
OVER TEN YEARS	0.0
AMORTIZED COST	3,068.0	2,645.8
Available for Sale - Fair Value
ONE YEAR OR LESS	640.9
ONE TO FIVE YEARS	2,143.0
FIVE TO TEN YEARS	134.1
OVER TEN YEARS	0.0
FAIR VALUE	2,918.0	2,479.4
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	864.8
ONE TO FIVE YEARS	4,724.3
FIVE TO TEN YEARS	56.7
OVER TEN YEARS	0.0
Amortized Cost	5,645.8	5,703.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	854.5
ONE TO FIVE YEARS	4,254.2
FIVE TO TEN YEARS	46.1
OVER TEN YEARS	0.0
Fair Value	5,154.8	5,268.2
Other Asset-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	1,191.8
ONE TO FIVE YEARS	2,732.6
FIVE TO TEN YEARS	1,106.5
OVER TEN YEARS	104.1
AMORTIZED COST	5,135.0	5,544.3
Available for Sale - Fair Value
ONE YEAR OR LESS	1,136.1
ONE TO FIVE YEARS	2,579.0
FIVE TO TEN YEARS	1,091.7
OVER TEN YEARS	102.8
FAIR VALUE	4,909.6	5,256.2
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	12.3
ONE TO FIVE YEARS	79.0
FIVE TO TEN YEARS	171.4
OVER TEN YEARS	25.3
Amortized Cost	288.0	263.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	12.3
ONE TO FIVE YEARS	78.8
FIVE TO TEN YEARS	171.3
OVER TEN YEARS	25.3
Fair Value	287.7	262.7
Other
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	55.4
ONE TO FIVE YEARS	326.0
FIVE TO TEN YEARS	32.7
OVER TEN YEARS	169.5
Amortized Cost	583.6	532.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	53.9
ONE TO FIVE YEARS	283.6
FIVE TO TEN YEARS	23.7
OVER TEN YEARS	55.8
Fair Value	417.0	375.2
Commercial Mortgage-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	37.8
ONE TO FIVE YEARS	771.9
FIVE TO TEN YEARS	155.7
OVER TEN YEARS	0.0
AMORTIZED COST	965.4	1,456.9
Available for Sale - Fair Value
ONE YEAR OR LESS	35.7
ONE TO FIVE YEARS	735.0
FIVE TO TEN YEARS	130.6
OVER TEN YEARS	0.0
FAIR VALUE	901.3	$ 1,387.8
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	37.6
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	37.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	36.8
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	$ 36.8