Long-Term Debt and Credit Facilities - Purchased Subordinated Debt (Details) - Consolidation, Eliminations [Member] - AGMH [Member] - AGUS [Member] - Junior Subordinated Debentures [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Principal amount repurchased	$ 3	$ 100	$ 28
Loss on extinguishment of debt	$ 1	$ 34	$ 9