Stockholders' Equity - Stock Repurchase Program (Details) shares in Thousands	Mar. 31, 2018 USD ($) shares
Class of Stock [Line Items]
Number of shares repurchased (in shares) | shares	2,526,399
Aggregate cost for shares repurchased	$ 9,671,848,000
Remaining amount authorized under the stock repurchase program	2,328,152,000
Common Stock
Class of Stock [Line Items]
Stock repurchase program, aggregate authorized amount	$ 12,000,000,000