Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Available for Sale - Amortized Cost
ONE YEAR OR LESS	$ 5,176.3
ONE TO FIVE YEARS	18,662.7
FIVE TO TEN YEARS	11,050.2
OVER TEN YEARS	1,963.0
AMORTIZED COST	36,852.2	$ 37,948.5
Available for Sale - Fair Value
ONE YEAR OR LESS	5,098.9
ONE TO FIVE YEARS	17,978.0
FIVE TO TEN YEARS	10,140.1
OVER TEN YEARS	1,800.9
FAIR VALUE	35,017.9	38,010.5
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	4,601.1
ONE TO FIVE YEARS	10,892.0
FIVE TO TEN YEARS	3,297.3
OVER TEN YEARS	1,322.2
Amortized Cost	20,112.6	23,564.5
Held to Maturity - Fair Value
ONE YEAR OR LESS	4,539.3
ONE TO FIVE YEARS	10,315.2
FIVE TO TEN YEARS	2,953.7
OVER TEN YEARS	1,117.3
Fair Value	18,925.5	23,315.4
U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	494.8
ONE TO FIVE YEARS	1,901.8
FIVE TO TEN YEARS	248.6
OVER TEN YEARS	0.0
AMORTIZED COST	2,645.2	2,406.2
Available for Sale - Fair Value
ONE YEAR OR LESS	495.9
ONE TO FIVE YEARS	1,873.4
FIVE TO TEN YEARS	219.1
OVER TEN YEARS	0.0
FAIR VALUE	2,588.4	2,426.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	56.9
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	56.9	47.0
Held to Maturity - Fair Value
ONE YEAR OR LESS	56.5
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	56.5	47.0
Obligations of States and Political Subdivisions
Available for Sale - Amortized Cost
ONE YEAR OR LESS	28.3
ONE TO FIVE YEARS	721.7
FIVE TO TEN YEARS	3,008.0
OVER TEN YEARS	125.1
AMORTIZED COST	3,883.1	3,841.0
Available for Sale - Fair Value
ONE YEAR OR LESS	28.2
ONE TO FIVE YEARS	689.0
FIVE TO TEN YEARS	2,632.3
OVER TEN YEARS	103.8
FAIR VALUE	3,453.3	3,876.1
Held to Maturity - Amortized Cost
Amortized Cost		0.8
Held to Maturity - Fair Value
Fair Value		0.8
Government Sponsored Agency
Available for Sale - Amortized Cost
ONE YEAR OR LESS	2,633.7
ONE TO FIVE YEARS	7,043.5
FIVE TO TEN YEARS	5,752.9
OVER TEN YEARS	1,721.2
AMORTIZED COST	17,151.3	18,092.1
Available for Sale - Fair Value
ONE YEAR OR LESS	2,578.1
ONE TO FIVE YEARS	6,852.2
FIVE TO TEN YEARS	5,398.1
OVER TEN YEARS	1,584.8
FAIR VALUE	16,413.2	18,075.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	640.5
ONE TO FIVE YEARS	1,865.3
FIVE TO TEN YEARS	2,094.9
OVER TEN YEARS	1,206.0
Amortized Cost	5,806.7	5,927.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	583.4
ONE TO FIVE YEARS	1,689.6
FIVE TO TEN YEARS	1,872.7
OVER TEN YEARS	1,078.6
Fair Value	5,224.3	5,822.6
Non-U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	104.2
ONE TO FIVE YEARS	214.9
FIVE TO TEN YEARS	77.1
OVER TEN YEARS	0.0
AMORTIZED COST	396.2	383.4
Available for Sale - Fair Value
ONE YEAR OR LESS	103.9
ONE TO FIVE YEARS	196.8
FIVE TO TEN YEARS	66.6
OVER TEN YEARS	0.0
FAIR VALUE	367.3	374.0
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	1,615.6
ONE TO FIVE YEARS	1,335.0
FIVE TO TEN YEARS	146.4
OVER TEN YEARS	0.0
Amortized Cost	3,097.0	5,773.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	1,614.0
ONE TO FIVE YEARS	1,269.4
FIVE TO TEN YEARS	134.2
OVER TEN YEARS	0.0
Fair Value	3,017.6	5,767.4
Corporate Debt
Available for Sale - Amortized Cost
ONE YEAR OR LESS	486.5
ONE TO FIVE YEARS	1,655.9
FIVE TO TEN YEARS	18.2
OVER TEN YEARS	2.8
AMORTIZED COST	2,163.4	2,319.8
Available for Sale - Fair Value
ONE YEAR OR LESS	484.2
ONE TO FIVE YEARS	1,585.7
FIVE TO TEN YEARS	15.6
OVER TEN YEARS	2.4
FAIR VALUE	2,087.9	2,341.7
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	228.8
ONE TO FIVE YEARS	629.6
FIVE TO TEN YEARS	14.8
OVER TEN YEARS	0.0
Amortized Cost	873.2	901.8
Held to Maturity - Fair Value
ONE YEAR OR LESS	228.0
ONE TO FIVE YEARS	600.0
FIVE TO TEN YEARS	12.6
OVER TEN YEARS	0.0
Fair Value	840.6	897.8
Covered Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	178.4
ONE TO FIVE YEARS	363.2
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
AMORTIZED COST	541.6	502.6
Available for Sale - Fair Value
ONE YEAR OR LESS	178.4
ONE TO FIVE YEARS	350.6
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
FAIR VALUE	529.0	505.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	489.6
ONE TO FIVE YEARS	1,678.4
FIVE TO TEN YEARS	510.3
OVER TEN YEARS	0.0
Amortized Cost	2,678.3	2,942.4
Held to Maturity - Fair Value
ONE YEAR OR LESS	489.5
ONE TO FIVE YEARS	1,630.4
FIVE TO TEN YEARS	457.3
OVER TEN YEARS	0.0
Fair Value	2,577.2	2,941.1
Certificates of Deposit
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	554.3
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	554.3	674.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	554.3
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	554.3	674.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	506.1
ONE TO FIVE YEARS	2,083.1
FIVE TO TEN YEARS	350.4
OVER TEN YEARS	0.0
AMORTIZED COST	2,939.6	3,052.4
Available for Sale - Fair Value
ONE YEAR OR LESS	506.8
ONE TO FIVE YEARS	1,979.7
FIVE TO TEN YEARS	307.3
OVER TEN YEARS	0.0
FAIR VALUE	2,793.8	3,045.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	932.8
ONE TO FIVE YEARS	4,752.8
FIVE TO TEN YEARS	380.2
OVER TEN YEARS	0.0
Amortized Cost	6,065.8	6,098.0
Held to Maturity - Fair Value
ONE YEAR OR LESS	931.7
ONE TO FIVE YEARS	4,523.6
FIVE TO TEN YEARS	338.8
OVER TEN YEARS	0.0
Fair Value	5,794.1	6,032.3
Other Asset-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	694.9
ONE TO FIVE YEARS	3,563.1
FIVE TO TEN YEARS	1,291.3
OVER TEN YEARS	113.9
AMORTIZED COST	5,663.2	5,962.0
Available for Sale - Fair Value
ONE YEAR OR LESS	676.0
ONE TO FIVE YEARS	3,382.1
FIVE TO TEN YEARS	1,223.5
OVER TEN YEARS	109.9
FAIR VALUE	5,391.5	5,941.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	58.1
ONE TO FIVE YEARS	344.8
FIVE TO TEN YEARS	93.2
OVER TEN YEARS	0.0
Amortized Cost	496.1	682.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	58.0
ONE TO FIVE YEARS	344.0
FIVE TO TEN YEARS	92.7
OVER TEN YEARS	0.0
Fair Value	494.7	683.6
Commercial Mortgage-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	49.4
ONE TO FIVE YEARS	1,115.5
FIVE TO TEN YEARS	303.7
OVER TEN YEARS	0.0
AMORTIZED COST	1,468.6	1,389.0
Available for Sale - Fair Value
ONE YEAR OR LESS	47.4
ONE TO FIVE YEARS	1,068.5
FIVE TO TEN YEARS	277.6
OVER TEN YEARS	0.0
FAIR VALUE	1,393.5	1,424.7
Other
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	24.5
ONE TO FIVE YEARS	286.1
FIVE TO TEN YEARS	57.5
OVER TEN YEARS	116.2
Amortized Cost	484.3	516.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	23.9
ONE TO FIVE YEARS	258.2
FIVE TO TEN YEARS	45.4
OVER TEN YEARS	38.7
Fair Value	$ 366.2	$ 448.1