先看一下Excess Reserve
Bloomberg 的图单位有误，应该读做1.305Trillion。大家可以从FRED Economic Data 从读数据。FRED上Excess Reserves 是monthly data，Bloomberg 从每天Fed Balance Sheet 推算出daily data。
从fractional reserve model角度看，钱还是很充裕的。理论上说只要Overnight Repo Rate 高于IOER (Interest Rate on Excess Reserves，目前1.80%/year)，特别是高于Fed Funds market rate，这些Excess Reserve就应该跑出来赚高一点的利息。
但银行监管不仅仅是Required Reserve Ratio（美国目前是10%），还有Basel III 国际监管框架（美国有自己的一套，Dodd-Frank Act），要求银行满足一定的Capital requirement，也就是银行的share-holder自己要有一定比例的肉在里面，称为Tier 1 capital。Tier 1 capital 不能低于 balance sheet 某个百分比 (4-6%)。太低了监管机构要找你麻烦。许多银行Tier 1 capital 已经在边缘，尽管有excess reserve也无法借出，只能放在Excess Reserve里赚一点点IOER。
JP Morgan的Jamie Dimon 说："We could not redeploy it into the repo market. We'd have been happy to do it," Dimon said Tuesday. "It's up to the regulators to decide if they want to recalibrate the kind of liquidity they expect us to keep in that account."
https://www.americanbanker.com/articles/jpmorgan-felt-barred-from-calming-repo-market-by-regulations
Dodd-Frank大帽子压着，Fed 没办法只能印钱消灾 --- balance sheet 尾巴又往上翘了
