Securities (Remaining Maturity of Securities Available for Sale and Held to Maturity) (Details) - USD ($) $ in Millions	Sep. 30, 2022	Dec. 31, 2021
Available for Sale - Amortized Cost
ONE YEAR OR LESS	$ 5,377.4
ONE TO FIVE YEARS	15,569.6
FIVE TO TEN YEARS	6,186.9
OVER TEN YEARS	1,135.7
AMORTIZED COST	28,269.6	$ 37,948.5
Available for Sale - Fair Value
ONE YEAR OR LESS	5,300.9
ONE TO FIVE YEARS	14,794.9
FIVE TO TEN YEARS	5,796.1
OVER TEN YEARS	1,087.4
FAIR VALUE	26,979.3	38,010.5
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	4,636.6
ONE TO FIVE YEARS	11,928.3
FIVE TO TEN YEARS	6,129.9
OVER TEN YEARS	2,555.0
Amortized Cost	25,249.8	23,564.5
Held to Maturity - Fair Value
ONE YEAR OR LESS	4,487.8
ONE TO FIVE YEARS	10,873.5
FIVE TO TEN YEARS	5,507.9
OVER TEN YEARS	2,195.7
Fair Value	23,064.9	23,315.4
U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	1,272.3
ONE TO FIVE YEARS	1,120.4
FIVE TO TEN YEARS	248.6
OVER TEN YEARS	0.0
AMORTIZED COST	2,641.3	2,406.2
Available for Sale - Fair Value
ONE YEAR OR LESS	1,274.8
ONE TO FIVE YEARS	1,059.4
FIVE TO TEN YEARS	209.8
OVER TEN YEARS	0.0
FAIR VALUE	2,544.0	2,426.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	57.9
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	57.9	47.0
Held to Maturity - Fair Value
ONE YEAR OR LESS	57.9
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	57.9	47.0
Obligations of States and Political Subdivisions
Available for Sale - Amortized Cost
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	146.6
FIVE TO TEN YEARS	774.7
OVER TEN YEARS	42.1
AMORTIZED COST	963.4	3,841.0
Available for Sale - Fair Value
ONE YEAR OR LESS	0.0
ONE TO FIVE YEARS	134.7
FIVE TO TEN YEARS	668.1
OVER TEN YEARS	35.1
FAIR VALUE	837.9	3,876.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	26.9
ONE TO FIVE YEARS	671.9
FIVE TO TEN YEARS	1,351.1
OVER TEN YEARS	508.6
Amortized Cost	2,558.5	0.8
Held to Maturity - Fair Value
ONE YEAR OR LESS	26.3
ONE TO FIVE YEARS	648.6
FIVE TO TEN YEARS	1,278.7
OVER TEN YEARS	471.4
Fair Value	2,425.0	0.8
Government Sponsored Agency
Available for Sale - Amortized Cost
ONE YEAR OR LESS	2,372.3
ONE TO FIVE YEARS	5,644.6
FIVE TO TEN YEARS	3,308.3
OVER TEN YEARS	867.7
AMORTIZED COST	12,192.9	18,092.1
Available for Sale - Fair Value
ONE YEAR OR LESS	2,331.9
ONE TO FIVE YEARS	5,527.7
FIVE TO TEN YEARS	3,205.4
OVER TEN YEARS	833.7
FAIR VALUE	11,898.7	18,075.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	949.3
ONE TO FIVE YEARS	2,991.7
FIVE TO TEN YEARS	3,784.6
OVER TEN YEARS	1,901.5
Amortized Cost	9,627.1	5,927.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	843.8
ONE TO FIVE YEARS	2,667.4
FIVE TO TEN YEARS	3,387.6
OVER TEN YEARS	1,679.1
Fair Value	8,577.9	5,822.6
Non-U.S. Government
Available for Sale - Amortized Cost
ONE YEAR OR LESS	32.8
ONE TO FIVE YEARS	200.6
FIVE TO TEN YEARS	71.8
OVER TEN YEARS	0.0
AMORTIZED COST	305.2	383.4
Available for Sale - Fair Value
ONE YEAR OR LESS	32.5
ONE TO FIVE YEARS	182.6
FIVE TO TEN YEARS	61.5
OVER TEN YEARS	0.0
FAIR VALUE	276.6	374.0
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	1,444.7
ONE TO FIVE YEARS	1,264.5
FIVE TO TEN YEARS	135.7
OVER TEN YEARS	0.0
Amortized Cost	2,844.9	5,773.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	1,444.1
ONE TO FIVE YEARS	1,153.1
FIVE TO TEN YEARS	113.5
OVER TEN YEARS	0.0
Fair Value	2,710.7	5,767.4
Corporate Debt
Available for Sale - Amortized Cost
ONE YEAR OR LESS	509.6
ONE TO FIVE YEARS	1,413.9
FIVE TO TEN YEARS	18.2
OVER TEN YEARS	1.9
AMORTIZED COST	1,943.6	2,319.8
Available for Sale - Fair Value
ONE YEAR OR LESS	502.0
ONE TO FIVE YEARS	1,322.6
FIVE TO TEN YEARS	14.4
OVER TEN YEARS	1.5
FAIR VALUE	1,840.5	2,341.7
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	206.3
ONE TO FIVE YEARS	578.0
FIVE TO TEN YEARS	13.9
OVER TEN YEARS	0.0
Amortized Cost	798.2	901.8
Held to Maturity - Fair Value
ONE YEAR OR LESS	205.1
ONE TO FIVE YEARS	533.5
FIVE TO TEN YEARS	11.0
OVER TEN YEARS	0.0
Fair Value	749.6	897.8
Covered Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	136.0
ONE TO FIVE YEARS	291.4
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
AMORTIZED COST	427.4	502.6
Available for Sale - Fair Value
ONE YEAR OR LESS	135.6
ONE TO FIVE YEARS	275.9
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
FAIR VALUE	411.5	505.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	509.4
ONE TO FIVE YEARS	1,489.7
FIVE TO TEN YEARS	467.2
OVER TEN YEARS	0.0
Amortized Cost	2,466.3	2,942.4
Held to Maturity - Fair Value
ONE YEAR OR LESS	507.3
ONE TO FIVE YEARS	1,417.3
FIVE TO TEN YEARS	397.3
OVER TEN YEARS	0.0
Fair Value	2,321.9	2,941.1
Certificates of Deposit
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	475.5
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Amortized Cost	475.5	674.7
Held to Maturity - Fair Value
ONE YEAR OR LESS	442.3
ONE TO FIVE YEARS	0.0
FIVE TO TEN YEARS	0.0
OVER TEN YEARS	0.0
Fair Value	442.3	674.7
Sub-Sovereign, Supranational and Non-U.S. Agency Bonds
Available for Sale - Amortized Cost
ONE YEAR OR LESS	358.1
ONE TO FIVE YEARS	2,070.3
FIVE TO TEN YEARS	233.7
OVER TEN YEARS	0.0
AMORTIZED COST	2,662.1	3,052.4
Available for Sale - Fair Value
ONE YEAR OR LESS	354.7
ONE TO FIVE YEARS	1,942.9
FIVE TO TEN YEARS	190.7
OVER TEN YEARS	0.0
FAIR VALUE	2,488.3	3,045.1
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	841.9
ONE TO FIVE YEARS	4,512.3
FIVE TO TEN YEARS	267.6
OVER TEN YEARS	0.0
Amortized Cost	5,621.8	6,098.0
Held to Maturity - Fair Value
ONE YEAR OR LESS	837.4
ONE TO FIVE YEARS	4,074.3
FIVE TO TEN YEARS	219.8
OVER TEN YEARS	0.0
Fair Value	5,131.5	6,032.3
Other Asset-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	688.1
ONE TO FIVE YEARS	3,478.5
FIVE TO TEN YEARS	1,246.1
OVER TEN YEARS	224.0
AMORTIZED COST	5,636.7	5,962.0
Available for Sale - Fair Value
ONE YEAR OR LESS	661.7
ONE TO FIVE YEARS	3,217.5
FIVE TO TEN YEARS	1,197.7
OVER TEN YEARS	217.1
FAIR VALUE	5,294.0	5,941.6
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	95.1
ONE TO FIVE YEARS	121.0
FIVE TO TEN YEARS	76.1
OVER TEN YEARS	0.0
Amortized Cost	292.2	682.6
Held to Maturity - Fair Value
ONE YEAR OR LESS	94.8
ONE TO FIVE YEARS	120.3
FIVE TO TEN YEARS	75.7
OVER TEN YEARS	0.0
Fair Value	290.8	683.6
Other
Held to Maturity - Amortized Cost
ONE YEAR OR LESS	29.6
ONE TO FIVE YEARS	299.2
FIVE TO TEN YEARS	33.7
OVER TEN YEARS	144.9
Amortized Cost	507.4	516.3
Held to Maturity - Fair Value
ONE YEAR OR LESS	28.8
ONE TO FIVE YEARS	259.0
FIVE TO TEN YEARS	24.3
OVER TEN YEARS	45.2
Fair Value	357.3	448.1
Commercial Mortgage-Backed
Available for Sale - Amortized Cost
ONE YEAR OR LESS	8.2
ONE TO FIVE YEARS	1,203.3
FIVE TO TEN YEARS	285.5
OVER TEN YEARS	0.0
AMORTIZED COST	1,497.0	1,389.0
Available for Sale - Fair Value
ONE YEAR OR LESS	7.7
ONE TO FIVE YEARS	1,131.6
FIVE TO TEN YEARS	248.5
OVER TEN YEARS	0.0
FAIR VALUE	$ 1,387.8	$ 1,424.7