Regulatory Capital and Other Regulatory Matters (Schedule of Regulatory Capital Amount and Ratios) (Details) - USD ($) $ / shares in Units, $ in Millions	Oct. 09, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier 1 capital to risk-weighted assets, required minimum		4.50%
Tier one capital to risk-weighted assets, required minimum		6.00%
Capital to risk-weighted assets, required minimum		8.00%
Common equity tier one capital conservation buffer		2.50%
Tier one leverage ratio, minimum		4.00%
BHC enhanced prudential standards, minimum		$ 100,000
BHC enhanced prudential standards, maximum		250,000
BHC stress test threshold		$ 50,000
Minimum capital conservation buffer		1.875%			1.25%
Minimum capital conservation buffer, increased percentage		2.50%
Increase (decrease) in share repurchase program		32.00%
Stock repurchase program, authorized amount		$ 1,000
Dividends declared, amount per common share		$ 0.15	$ 0.13	$ 0.13	$ 0.12	$ 0.12	$ 0.08	$ 0.08	$ 0.08	$ 0.08
Parent company
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier 1 capital to risk-weighted assets, required minimum		4.50%
Tier one capital to risk-weighted assets, required minimum		6.00%
Capital to risk-weighted assets, required minimum		8.00%
Tier one leverage ratio, minimum		4.00%
Common equity tier one capital to risk-weighted assets, amount		$ 13,376			$ 13,237
Common equity tier one capital to risk-weighted assets, ratio		9.41%			9.53%
Tier one capital to risk-weighted assets, amount		$ 15,810			$ 15,628
Tier one capital to risk-weighted assets, ratio		11.12%			11.25%
Tier one capital to risk-weighted assets, well-capitalized minimum		6.00%
Capital to risk-weighted assets, amount		$ 18,029			$ 17,974
Capital to risk-weighted assets, ratio		12.68%			12.94%
Capital to risk weighted assets, well-capitalzed minimum		10.00%
Tier one leverage to adjusted quarterly average assets, amount		$ 15,810			$ 15,628
Tier one leverage to adjusted quarterly average assets, ratio		9.23%			9.53%
Subsidiaries
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common equity tier 1 capital to risk-weighted assets, required minimum		4.50%
Tier one capital to risk-weighted assets, required minimum		6.00%
Capital to risk-weighted assets, required minimum		8.00%
Tier one leverage ratio, minimum		4.00%
Common equity tier one capital to risk-weighted assets, amount		$ 16,590			$ 17,059
Common equity tier one capital to risk-weighted assets, ratio		13.32%			15.04%
Common equity tier one capital to risk-weighted assets, well-capitalized minimum		6.50%
Tier one capital to risk-weighted assets, amount		$ 16,590			$ 17,059
Tier one capital to risk-weighted assets, ratio		13.32%			15.04%
Tier one capital to risk-weighted assets, well-capitalized minimum		8.00%
Capital to risk-weighted assets, amount		$ 17,606			$ 17,886
Capital to risk-weighted assets, ratio		14.13%			15.77%
Capital to risk weighted assets, well-capitalzed minimum		10.00%
Tier one leverage to adjusted quarterly average assets, amount		$ 16,590			$ 17,059
Tier one leverage to adjusted quarterly average assets, ratio		11.27%			12.87%
Tier one leverage to adjusted quarterly average assets, well-capitalized minimum		5.00%
Subsequent event
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends declared, amount per common share	$ 0.15