Shareholders' Equity (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	$ 2,394	$ 2,971	$ 2,293	$ 2,731
Net income	223	251	448	674
Other comprehensive loss	(108)	(10)	(126)	(12)
Share-based compensation	15	17	34	36
Shares issued under stock plans	22	12	17	2
Purchases of treasury stock	0	(391)	(120)	(789)
Balance at end of period	$ 2,546	$ 2,850	$ 2,546	$ 2,850
Common Shares
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period (in shares)	791	791	791	791
Balance at beginning of period	$ 8	$ 8	$ 8	$ 8
Balance at end of period (in shares)	791	791	791	791
Balance at end of period	$ 8	$ 8	$ 8	$ 8
Treasury Stock
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period (in shares)	399	380	399	376
Balance at beginning of period	$ (10,423)	$ (8,857)	$ (10,340)	$ (8,494)
Shares issued under stock plans (in shares)	0	0	(2)	(2)
Shares issued under stock plans	$ 15	$ 11	$ 52	$ 46
Purchases of treasury stock (in shares)	0	5	2	11
Purchases of treasury stock	$ 0	$ (391)	$ (120)	$ (789)
Balance at end of period (in shares)	399	385	399	385
Balance at end of period	$ (10,408)	$ (9,237)	$ (10,408)	$ (9,237)
Additional Paid-In Capital
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	1,034	1,005	1,057	1,031
Share-based compensation	15	17	34	36
Shares issued under stock plans	7	1	(35)	(44)
Balance at end of period	1,056	1,023	1,056	1,023
Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	(85)	(56)	(67)	(54)
Other comprehensive loss	(108)	(10)	(126)	(12)
Balance at end of period	(193)	(66)	(193)	(66)
Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Balance at beginning of period	11,860	10,871	11,635	10,240
Net income	223	251	448	674
Balance at end of period	$ 12,083	$ 11,122	$ 12,083	$ 11,122
Accounting Standards Update 2014-09
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment of ASU adoption					$ 208
Accounting Standards Update 2014-09 | Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment of ASU adoption					208
Accounting Standards Update 2018-02 | Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment of ASU adoption					(3)
Accounting Standards Update 2018-02 | Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment of ASU adoption					3
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2017-12 | Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment of ASU adoption					3	$ 3
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2017-12 | Retained Earnings
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment of ASU adoption					$ (3)
New Accounting Pronouncement, Early Adoption, Effect | Accounting Standards Update 2018-02 | Accumulated Other Comprehensive Loss
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative-effect adjustment of ASU adoption						$ (3)