Derivative Instruments (Offsetting Assets and Liabilities) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Derivative Assets
Gross Amounts of Recognized Financial Instruments	$ 14,303	$ 10,407
Gross Amounts Offset in the Statements of Financial Position	(13,519)	(9,331)
Net Amounts Presented in the Statements of Financial Position	784	1,076
Financial Instruments/Collateral	(607)	(614)
Net Amount	177	462
Securities purchased under agreement to resell
Gross Amounts of Recognized Financial Instruments	1,012	986
Gross Amounts Offset in the Statements of Financial Position	0	0
Net Amounts Presented in the Statements of Financial Position	1,012	986
Financial Instruments/Collateral	(1,012)	(986)
Net Amount	0	0
Total Assets
Gross Amounts of Recognized Financial Instruments	15,315	11,393
Gross Amounts Offset in the Statements of Financial Position	(13,519)	(9,331)
Net Amounts Presented in the Statements of Financial Position	1,796	2,062
Financial Instruments/Collateral	(1,619)	(1,600)
Net Amount	177	462
Derivative Liabilities
Gross Amounts of Recognized Financial Instruments	7,528	5,387
Gross Amounts Offset in the Statement of Financial Position	(6,705)	(5,281)
Net Amounts Presented in the Statement of Financial Position	823	106
Financial Instruments/Collateral	(244)	(45)
Net Amount	579	61
Securities sold under agreement to repurchase
Gross Amounts of Recognized Financial Instruments	9,681	9,950
Gross Amounts Offset in the Statement of Financial Position	0	0
Net Amounts Presented in the Statement of Financial Position	9,681	9,950
Financial Instruments/Collateral	(9,681)	(9,950)
Net Amount	0	0
Total Liabilities
Gross Amounts of Recognized Financial Instruments	17,209	15,337
Gross Amounts Offset in the Statement of Financial Position	(6,705)	(5,281)
Net Amounts Presented in the Statement of Financial Position	10,504	10,056
Financial Instruments/Collateral	(9,925)	(9,995)
Net Amount	$ 579	$ 61