$18 Billion dollars, possibly much more...
It's probably enough money to convert dozens and dozens of the world's largest ships from burning filthy Bunker fuels to burning something vastly, unimaginably, mind-bogglingly cleaner, such as diesel.
If anyone was in charge of the larger picture, then that somebody would take the equivalent total fine + follow-on cost money from VW, allow them a 'pass' (an 'Indulgence') on the existing fleet of cars (it'll sort itself out in a decade anyway), and use the vast pile of money thus released to more effective ends - such as fixing Bunker powered ships.
Unfortunately, nobody is in charge. So billions will be spent ineffectively. And Bunker fuel powered ships in any given harbour will go uncorrected, hundreds of thousands of times worse in the NOx sense than the entire fleet of VWs.