Parent Company - Condensed Balance Sheets (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Other assets	$ 440	$ 543
Total assets	15,334	14,326
Other liabilities	556	511
Total liabilities	8,629	7,674
Total shareholders’ equity	6,684	6,645	$ 6,555	$ 6,839
Total liabilities, redeemable noncontrolling interests and shareholders’ equity	15,334	14,326
Assured Guaranty Ltd. (Parent)
Condensed Balance Sheet Statements, Captions [Line Items]
Investments and cash	190	135
Investments in subsidiaries	6,432	6,450
Dividends receivable from affiliate	0	40
Other assets	38	31
Total assets	6,660	6,656
Other liabilities	17	17
Total liabilities	17	17
Total shareholders’ equity	6,643	6,639
Total liabilities, redeemable noncontrolling interests and shareholders’ equity	$ 6,660	$ 6,656