The maximum weight you can carry in Minecraft is complicated. For starters, ice is better than anything else because the max amount of blocks one water can make is ~537 million blocks^, and ice stacks to 64. Then you use shulkers and stuff. A cubic meter of water is ~1000 KG, so the max weight Steve can carry in two hands is...
45,778,176,000,000,000 kilograms (45 quadrillion kilograms)
Oh yeah for American units it's (very approximately) 99,208,017,983,194,912 pounds It's probably more than 100 quadrillion though