More than 7,000 flights were behind schedule by Monday night, many of those in New York, Washington and Chicago as people struggled to travel before Christmas.
At least 11 people have been killed in the storm.
States kept emergency shelters open for people who would be without power, some through Christmas.
About 2,50,000 of the people without power were in Michigan, whose largest utilities said it'll be days before power is restored because of the difficulty of working around broken lines.
In Maine, the number of customers without power spiked to more than 1,00,000.
Untreated roads and sidewalks will remain a slippery, dangerous mess.