Mastercard Inc. vaulted into $400 billion territory for the first time Wednesday in a testament to confidence about consumer spending and momentum for digital payment methods. Shares of Mastercard MA, +1.34$401.6 billion, according to Dow Jones Market Data. The company is the 15th-largest public company in the U.S. by market value, ahead of Exxon Mobil Corp. XOM, -0.98% and Johnson & Johnson JNJ, +0.15%. Rival Visa Inc. V, +0.47% si ...