Benefit Plans - Narrative (Details) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2018	Dec. 31, 2017 USD ($) year	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined benefit plan, number of highest consecutive years of earnings | year			5
Defined benefit plan, final years of employment subject to earnings test			10 years
Net asset values			$ 6,152	$ 4,824
Defined contribution plan, employee contribution percentage, minimum			1.00%
Defined contribution plan, employee contribution percentage, maximum			50.00%
Defined contribution plan, minimum age of employees covered			21 years
Defined contribution plan, minimum years of service of employees covered			1 year
Defined contribution plan, employer matching contribution, percentage of employee compensation, maximum			6.00%
Defined contribution plan, employer contribution expense			$ 133	129	$ 114
U.S. Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net asset values			2,503	1,892
International Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net asset values			1,130	839
Fixed Income Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net asset values			$ 2,452	$ 1,914
Forecast
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average expected long-term rate of return on plan assets		7.00%
Qualified Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Weighted average expected long-term rate of return on plan assets			7.00%	7.00%	7.50%
Net asset values			$ 6,309	$ 5,044	$ 4,369
Qualified Plan | Alternative Investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Net asset values			$ 105	$ 199
Qualified Plan | Subsequent Event
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Discretionary contributions made to the qualified pension plan	$ 144
Min | Qualified Plan | U.S. Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage			30.00%
Min | Qualified Plan | International Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage			11.00%
Min | Qualified Plan | Fixed Income Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage			35.00%
Min | Qualified Plan | Alternative Investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage			0.00%
Max | Qualified Plan | BB&T Corporation:
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage			10.00%
Max | Qualified Plan | U.S. Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage			50.00%
Max | Qualified Plan | International Equity Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage			18.00%
Max | Qualified Plan | Fixed Income Securities
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage			53.00%
Max | Qualified Plan | Alternative Investments
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage			14.00%