Accrued Expenses and Other Liabilities (Schedule of Accrued Expenses and Other Liabilities) (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Accounts Payable and Accrued Liabilities [Abstract]
Accounts Payable	$ 369	$ 746
Accrued Employee Benefits	188	248
Liability for Claims and Claims Adjustment Expense	149	140	$ 179	$ 149
Derivative Liability, Fair Value, Gross Liability	65	41
Cash collateral received from counterparties	39	17
Deferred Revenue	28	32
Other Accrued Liabilities	673	556
Accounts Payable and Accrued Liabilities	$ 1,511	$ 1,780