Stock Plans (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Restricted Stock And Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period, in years	3 years
Pre-tax compensation expense	$ 51	$ 46	$ 49
Deferred tax benefit	20	18	19
Unamortized compensation expense	$ 68
Weighted-average period of recognition, in years	2 years
Weighted-average grant date fair value	$ 65	$ 53	$ 49
Weighted-average grant date fair value, per share	$ 54.54	$ 36.75	$ 33.76
Total fair value vested	$ 85	$ 86	$ 89
Common Stock [Member] | 2015 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares issuable under the stock compensation plan (in shares)	40,000,000
Shares available to be granted (in shares)	39,994,482
Common Stock [Member] | 2015 Directors Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum number of shares issuable under the stock compensation plan (in shares)	1,000,000
Shares available to be granted (in shares)	993,284