Common Share Repurchases (details) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2016 USD ($) $ / shares shares	Sep. 30, 2016 USD ($) $ / shares shares
Common Share Repurchases disclosure
Number of shares repurchased (in shares) | shares	4.7	14.7
Cost of shares repurchased	$ 550	$ 1,650
Average cost per share repurchased | $ / shares	$ 117.25	$ 112.50
Remaining capacity under share repurchase authorization	$ 1,680	$ 1,680
Number of shares acquired to cover tax withholding costs and exercise costs (in shares) | shares	0.1	0.6
Cost of shares acquired to cover tax withholding costs and exercise costs	$ 12	$ 71