Borrowings (Long-term Debt Including Unamortized Debt Discounts and Premiums) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Senior Notes	$ 2,558	$ 2,553
Medium-Term Notes, Series A	250	249
Finance lease obligation	68	75
Total long-term debt	2,876	2,877	[1]
Debt issuance costs	10
Liabilities	$ 206,962	170,303	[1]
Restatement Adjustment [Member] | Accounting Standards Update 2015-03 [Member]
Debt Instrument [Line Items]
Total long-term debt		(13)
Debt issuance costs		(13)
Liabilities		$ (13)

[1] Adjusted for the retrospective adoption of ASU 2015-03. See New Accounting Standards in Note 2 for additional information.