Stockholders' Equity - Narrative (Details) $ / shares in Units, shares in Millions	1 Months Ended			3 Months Ended				9 Months Ended
	Dec. 31, 2018 USD ($) vote $ / shares shares	Jul. 31, 2018 $ / shares	Mar. 31, 2018 USD ($) shares	Dec. 31, 2018 USD ($) vote $ / shares shares	Sep. 30, 2018 USD ($) $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Dec. 31, 2017 $ / shares	Dec. 31, 2018 USD ($) vote $ / shares	Dec. 31, 2017 $ / shares	May 31, 2018 USD ($)
Accelerated Share Repurchases [Line Items]
Number of votes per share of common stock permitted on proposals presented to stockholders (vote) | vote	1			1				1
Dividends declared per common share (in dollars per share) | $ / shares		$ 0.39		$ 0.39		$ 0.34	$ 0.34	$ 1.12	$ 0.96
Authorized repurchase amount (up to)										$ 4,000,000,000.0
Common stock repurchased (shares) | shares				2.0	4.6	2.0
Shares repurchased during period				$ 250,000,000	$ 580,000,000	$ 297,000,000
Average price per share of shares repurchased (in usd per share) | $ / shares				$ 125.53	$ 127.39	$ 147.92
Authorized amount available for future repurchases	$ 3,700,000,000			$ 3,700,000,000				$ 3,700,000,000
Treasury shares retired (shares) | shares				5.0
Treasury shares retired, value				$ 542,000,000
Accelerated Share Repurchase
Accelerated Share Repurchases [Line Items]
Authorized repurchase amount (up to)	$ 250,000,000		$ 500,000,000	250,000,000				$ 250,000,000
Common stock repurchased (shares) | shares	1.6		2.5			1.0
Value of shares repurchased under the ASR program	$ 200,000,000
Initial price per share of initial number of shares repurchased under ASR program (in usd per share) | $ / shares	$ 122.15
Average price per share of shares repurchased (in usd per share) | $ / shares						$ 143.66
Retained Earnings
Accelerated Share Repurchases [Line Items]
Treasury shares retired, value				472,000,000
Additional Paid-in Capital
Accelerated Share Repurchases [Line Items]
Treasury shares retired, value				$ 70,000,000