Share Repurchase Programs and Dividends - Share Repurchase Programs (Details) $ / shares in Units, shares in Millions	3 Months Ended	6 Months Ended	48 Months Ended
	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) program $ / shares shares	Apr. 30, 2018 USD ($)
Equity, Class of Treasury Stock [Line Items]
Stock repurchase programs, authorized amount	$ 13,000,000,000	$ 13,000,000,000	$ 13,000,000,000
Number of share repurchase programs authorized | program			7
Stock repurchase programs, remaining authorized amount	$ 1,700,000,000	$ 1,700,000,000	$ 1,700,000,000
Stock repurchased (in shares) | shares	8.2	16.6	278.9
Aggregate stock repurchase price	$ 350,000,000	$ 800,000,000	$ 11,300,000,000
Average cost per share (in dollars per share) | $ / shares	$ 42.81	$ 48.15	$ 40.69
Share Repurchase Program April 2018 [Member]
Equity, Class of Treasury Stock [Line Items]
Stock repurchase programs, authorized amount				$ 2,000,000,000.0