Because it is a system guarantee. €400 billion is roughly the amount of liabilities that the 6 banks have and the amount isn't set in stone. Thats just the estimate. Likely to be more! They couldn't just say €50 billion because the market wouldn't know what liabilities were guaranteed and what weren't.
Thanks for clarifying that. Makes sense now.
I still like the Swedish solution! ;-)
Europe is now saying that countries shouldn't act unilaterally in this crisis. Will be interesting to see if they can impose their will on this one.
D.