Commitments and Contingencies (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Feb. 20, 2018
Commitments and Contingencies Disclosure [Abstract]
Standby letters of credit and guarantees outstanding	$ 174,000,000	$ 226,000,000
Subsidiary payment obligations demand for payment				$ 0
Total Minimum Commitments [Abstract]
2018	1,855,005,000
2019	1,068,994,000
2020	800,078,000
2021	567,840,000
2022	478,480,000
2023 and beyond	944,911,000
Total Minimum Commitments	5,715,308,000
Rental expenses associated with existing leases	$ 200,000,000	$ 204,000,000	$ 229,000,000