Income Taxes (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Total UTB that, if recognized, would impact the effective income tax rate as of the end of the year		$ 20
Decrease of unrecognized tax benefit	330
Loss carryforwards, charitable contribution		219
Tax benefit from employee stock plans		24
Income Tax Expense Ratemaking		235
Charitable Contribution Carryforward Expiration Date [Minimum]		Dec. 31, 2015
Charitable Contribution Carryforward Expiration Date [Maximum]		Dec. 31, 2019
Minimum [Member]
Net operating loss expiration year		Dec. 31, 2033
Maximum [Member]
Net operating loss expiration year		Dec. 31, 2034
State [Member]
Net operating loss carryforwards		123
Tax credit carryforward, amount		30
Tax Credit Carryforward Expiration Date [Maximum]		Dec. 31, 2024
Federal [Member]
Net operating loss carryforwards		4,100
Tax credit carryforwards, expiration amount		$ 77
Tax Credit Carryforward Expiration Date [Minimum]		Dec. 31, 2029
Tax Credit Carryforward Expiration Date [Maximum]		Dec. 31, 2034