Cash and Money Market Investments (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Assets [Member] | Federal Funds Sold and Securities Borrowed or Purchased under Agreements to Resell [Member]
Gain (Loss) on Securities [Line Items]
Gross amounts recognized	$ 694	$ 1,461
Gross amounts offset in the balance sheet	(210)	0
Net amounts presented in the balance sheet	484	1,461
Gross amounts not offset in the balance sheet	0	0
Cash Collateral Received/Pledged	0	0
Net amount	484	1,461
Assets [Member] | Derivative Financial Instruments, Assets [Member]
Gain (Loss) on Securities [Line Items]
Gross amounts recognized	153	45
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	153	45
Gross amounts not offset in the balance sheet	(6)	(35)
Cash Collateral Received/Pledged	0	(3)
Net amount	147	7
Assets [Member] | Assets, Total [Member]
Gain (Loss) on Securities [Line Items]
Gross amounts recognized	847	1,506
Gross amounts offset in the balance sheet	(210)	0
Net amounts presented in the balance sheet	637	1,506
Gross amounts not offset in the balance sheet	(6)	(35)
Cash Collateral Received/Pledged	0	(3)
Net amount	631	1,468
Other Liabilities [Member] | Federal Funds Purchased and Securities Sold under Agreements to Repurchase [Member]
Gain (Loss) on Securities [Line Items]
Gross amounts recognized	2,263	5,653
Gross amounts offset in the balance sheet	(210)	0
Net amounts presented in the balance sheet	2,053	5,653
Gross amounts not offset in the balance sheet	0	0
Cash Collateral Received/Pledged	0	0
Net amount	2,053	5,653
Other Liabilities [Member] | Derivative Financial Instruments, Liabilities [Member]
Gain (Loss) on Securities [Line Items]
Gross amounts recognized	19	39
Gross amounts offset in the balance sheet	0	0
Net amounts presented in the balance sheet	19	39
Gross amounts not offset in the balance sheet	(6)	(35)
Cash Collateral Received/Pledged	(10)	(1)
Net amount	3	3
Other Liabilities [Member] | Liabilities, Total [Member]
Gain (Loss) on Securities [Line Items]
Gross amounts recognized	2,282	5,692
Gross amounts offset in the balance sheet	(210)	0
Net amounts presented in the balance sheet	2,072	5,692
Gross amounts not offset in the balance sheet	(6)	(35)
Cash Collateral Received/Pledged	(10)	(1)
Net amount	$ 2,056	$ 5,656