Investments (Schedule of Investment Securities) (Details) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019
Investment Holdings [Line Items]
Investment securities		$ 10,782	$ 10,595
U.S. Treasury Securities [Member]
Investment Holdings [Line Items]
Investment securities	[1]	10,110	9,906
Derivative collateral		206	121
Residential Mortgage-Backed Securities - Agency [Member]
Investment Holdings [Line Items]
Investment securities	[2]	$ 672	$ 689

[1] Includes $206 million and $121 million of U.S. Treasury securities pledged as swap collateral as of March 31, 2020 and December 31, 2019, respectively.

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