Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Earnings Per Share [Abstract]
Shareholders' net income	$ 144	$ 772	$ 806	$ 915	$ 266	$ 560	$ 813	$ 598	$ 2,637	$ 2,237	$ 1,867
Shares:
Weighted average									246,652,000	250,892,000	255,360,000
Common stock equivalents									3,573,000	4,180,000	4,287,000
Total shares									250,225,000	255,072,000	259,647,000
EPS, basic	$ 0.56	$ 3.18	$ 3.32	$ 3.78	$ 1.09	$ 2.25	$ 3.2	$ 2.34	$ 10.69	$ 8.92	$ 7.31
EPS, effect of dilution									(0.15)	(0.15)	(0.12)
EPS, diluted	$ 0.55	$ 3.14	$ 3.29	$ 3.72	$ 1.07	$ 2.21	$ 3.15	$ 2.3	$ 10.54	$ 8.77	$ 7.19
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive options									900,000	900,000	2,300,000
Common shares held in Treasury	570,000				0				570,000	0	0