Regulatory Capital and Other Regulatory Matters (Schedule of Regulatory Capital Amount and Ratios) (Details) - USD ($) $ / shares in Units, $ in Millions	Jul. 13, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Aug. 22, 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 Required for Capital Adequacy to Risk-weighted Assets		4.50%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		6.00%
Capital Required for Capital Adequacy to Risk Weighted Assets		8.00%
Common equity Tier 1 capital conservation buffer		2.50%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets		4.00%
BHC Enhanced Prudential Standards, Minimum		$ 100,000
BHC Enhanced Prudential Standards, Maximum		250,000
BHC Stress Test Threshold		50,000
Federal Reserve Bank Stock		$ 447		$ 445
Minimum Capital Conservation Buffer		1.875%		1.25%
Increased Minimum Capital Conservation Buffer		2.50%
Increase (decrease) in share repurchase program		32.00%
Stock Repurchase Program, Authorized Amount		$ 1,000
Dividends Payable, Amount Per Share		$ 0.13	$ 0.13	$ 0.12	$ 0.12		$ 0.08	$ 0.08	$ 0.08	$ 0.08
Parent Company [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Capital Required for Capital Adequacy to Risk-weighted Assets		4.50%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		6.00%
Capital Required for Capital Adequacy to Risk Weighted Assets		8.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets		4.00%
Common Equity Tier 1 Capital		$ 13,265		$ 13,237
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets		9.37%		9.53%
Tier One Risk Based Capital		$ 15,698		$ 15,628
Tier One Risk Based Capital to Risk Weighted Assets		11.09%		11.25%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets		6.00%
Capital		$ 17,926		$ 17,974
Capital to Risk Weighted Assets		12.66%		12.94%
Capital Required to be Well Capitalized to Risk Weighted Assets		10.00%
Tier One Leverage Capital		$ 15,698		$ 15,628
Tier One Leverage Capital to Average Assets		9.21%		9.53%
Subsidiaries [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Common Equity Tier 1 Capital Required for Capital Adequacy to Risk-weighted Assets		4.50%
Tier One Risk Based Capital Required for Capital Adequacy to Risk Weighted Assets		6.00%
Capital Required for Capital Adequacy to Risk Weighted Assets		8.00%
Tier One Leverage Capital Required for Capital Adequacy to Average Assets		4.00%				15.00%
Common Equity Tier 1 Capital		$ 16,591		$ 17,059
Percentage of Common Equity Tier 1 Capital to Risk-weighted Assets		13.65%		15.04%
Common Equity Tier 1 Capital Required to be Well Capitalized to Risk-weighted Assets		6.50%
Tier One Risk Based Capital		$ 16,591		$ 17,059
Tier One Risk Based Capital to Risk Weighted Assets		13.65%		15.04%
Tier One Risk Based Capital Required to be Well Capitalized to Risk Weighted Assets		8.00%
Capital		$ 17,557		$ 17,886
Capital to Risk Weighted Assets		14.45%		15.77%
Capital Required to be Well Capitalized to Risk Weighted Assets		10.00%
Tier One Leverage Capital		$ 16,591		$ 17,059
Tier One Leverage Capital to Average Assets		11.50%		12.87%
Tier One Leverage Capital Required to be Well Capitalized to Average Assets		5.00%
Subsequent Event [Member]
Compliance with Regulatory Capital Requirements under Banking Regulations [Line Items]
Dividends Payable, Amount Per Share	$ 0.15
Increase (Decrease) in Dividends Payable, per share	$ 0.02
Increase (Decrease) in Dividends Payable	15.00%