Stock Compensation Plans and Other Compensation Arrangements (Details 2) - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock Option Activity
Shares under option - exercised	(0.2)
Shares under option - outstanding at period end	0.1	0.3
Stock Options, Vested and Expected to Vest at Period End
Total intrinsic value of stock options exercised	$ 18	$ 94	$ 118
Aggregate intrinsic value - outstanding at period end	$ 20	$ 28	$ 101