Investments (Schedule of Investment Securities) (Details) - USD ($) $ in Millions		Jun. 30, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Other short-term investments		$ 2,549	$ 0
Investment securities		10,485	10,595
US Treasury Bill Securities [Member]
Investment Holdings [Line Items]
Other short-term investments	[1]	2,549	0
U.S. Treasury Securities [Member]
Investment Holdings [Line Items]
Investment securities	[2]	9,838	9,906
Derivative collateral		159	121
Residential Mortgage-Backed Securities - Agency [Member]
Investment Holdings [Line Items]
Investment securities	[3]	$ 647	$ 689

[1] Includes U.S. Treasury bills with maturity dates greater than 90 days but less than one year at the time of acquisition.

[2] Includes $159 million and $121 million of U.S. Treasury securities pledged as swap collateral as of June 30, 2020 and December 31, 2019, respectively.

[3] Consists of residential mortgage-backed securities issued by Fannie Mae, Freddie Mac and Ginnie Mae.