Offsetting Assets and Liabilities (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell [Member] | Assets [Member]
Offsetting Assets [Line Items]
Net amount	$ 438	$ 1,461
Gross amounts recognized	739	1,461
Gross amounts offset in the balance sheet	(301)	0
Net amounts presented in the balance sheet	438	1,461
Gross amounts not offset in the balance sheet	0	0
Cash Collateral Received/Pledged	0	0
Derivative Financial Instruments, Assets [Member] | Assets [Member]
Offsetting Assets [Line Items]
Net amount	56	7
Gross amounts recognized	82	45
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	82	45
Gross amounts not offset in the balance sheet	(21)	(35)
Cash Collateral Received/Pledged	(5)	(3)
Assets, Total [Member] | Assets [Member]
Offsetting Assets [Line Items]
Net amount	494	1,468
Gross amounts recognized	821	1,506
Gross amounts offset in the balance sheet	(301)	0
Net amounts presented in the balance sheet	520	1,506
Gross amounts not offset in the balance sheet	(21)	(35)
Cash Collateral Received/Pledged	(5)	(3)
Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Member] | Other Liabilities [Member]
Offsetting Assets [Line Items]
Net amount	4,944	5,653
Gross amounts recognized	5,245	5,653
Gross amounts offset in the balance sheet	(301)	0
Net amounts presented in the balance sheet	4,944	5,653
Gross amounts not offset in the balance sheet	0	0
Cash Collateral Received/Pledged	0	0
Derivative Financial Instruments, Liabilities [Member] | Other Liabilities [Member]
Offsetting Assets [Line Items]
Net amount	4	3
Gross amounts recognized	25	39
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	25	39
Gross amounts not offset in the balance sheet	(21)	(35)
Cash Collateral Received/Pledged	0	(1)
Liabilities, Total [Member] | Other Liabilities [Member]
Offsetting Assets [Line Items]
Net amount	4,948	5,656
Gross amounts recognized	5,270	5,692
Gross amounts offset in the balance sheet	(301)	0
Net amounts presented in the balance sheet	4,969	5,692
Gross amounts not offset in the balance sheet	(21)	(35)
Cash Collateral Received/Pledged	$ 0	$ (1)