Capital and Mandatorily Redeemable Capital Stock (Regulatory Capital Rules and Requirements) (Details) - USD ($) $ in Millions		Jun. 30, 2019	Dec. 31, 2018
Capital [Abstract]
Risk-based capital, Required		$ 1,509	$ 1,654
Risk-based capital, Actual		$ 7,335	$ 7,597
Total regulatory capital ratio, Required		4.00%	4.00%
Total regulatory capital ratio, Actual		4.90%	4.92%
Total regulatory capital, Required	[1]	$ 5,988	$ 6,179
Total regulatory capital, Actual	[1]	$ 7,335	$ 7,597
Leverage capital ratio, Required		5.00%	5.00%
Leverage capital ratio, Actual		7.35%	7.38%
Leverage capital, Required		$ 7,485	$ 7,724
Leverage capital, Actual		$ 11,002	$ 11,396

[1] Total regulatory capital does not include accumulated other comprehensive income, but does include mandatorily redeemable capital stock.