Interest (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Interest [Abstract]
Interest Expense on Debt	$ 267	$ 296	$ 497
The Bow Office Building	63	62	65
Capital Leases	20	24	28
Other	13	15	24
Interest	$ 363	$ 397	$ 614