Long-Term Debt (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Nov. 30, 2015	Mar. 31, 2015
Debt Instrument [Line Items]
Long-term debt instruments		$ 27,071	$ 15,960
Debt due within one year		(1,487)	0
Reclassified from short-term debt		8,000	8,000
Total long-term debt		33,584	23,960
Long-term debt maturing 2016		1,487
Long-term debt maturing 2017		6,187
Long-term debt maturing 2018		5,836
Long-term debt maturing 2019		2,650
Long-term debt maturing 2020		4,054
Long-term debt maturing after 2020		6,857
Notes Payable [Member] | 3.191% notes due 2023 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 2,250	2,250
Interest rate		3.191%
Notes Payable [Member] | Floating rate notes due 2017 (0.555%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	[1]	$ 2,050	650
Interest rate		0.555%
Notes Payable [Member] | 1.104% notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 2,000	2,000
Interest rate		1.104%
Notes Payable [Member] | 1.718% notes due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 2,000	2,000
Interest rate		1.718%
Notes Payable [Member] | 2.355% notes due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 2,000	2,000
Interest rate		2.355%
Notes Payable [Member] | 1.365% notes due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 1,750	0
Interest rate		1.365%
Notes Payable [Member] | 1.961% notes due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 1,750	0
Interest rate		1.961%
Notes Payable [Member] | 4.95% notes due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 1,500	1,500
Interest rate		4.95%
Notes Payable [Member] | 1.790% notes due 2018 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 1,250	0
Interest rate		1.79%
Notes Payable [Member] | 2.419% notes due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 1,250	0
Interest rate		2.419%
Notes Payable [Member] | 1.345% notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 1,100	1,100
Interest rate		1.345%
Notes Payable [Member] | 1.344% notes due 2017 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 1,000	0
Interest rate		1.344%
Notes Payable [Member] | 2.427% notes due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 1,000	1,000
Interest rate		2.427%
Notes Payable [Member] | Floating rate notes due 2018 (0.676%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	[1]	$ 800	0
Interest rate		0.676%
Notes Payable [Member] | 0.889% notes due 2016 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 750	750
Interest rate		0.889%
Notes Payable [Member] | 2.193% notes due 2019 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 750	750
Interest rate		2.193%
Notes Payable [Member] | 3.326% notes due 2025 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 750	0
Interest rate		3.326%
Notes Payable [Member] | 2.411% notes due 2022 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 700	0
Interest rate		2.411%
Notes Payable [Member] | Floating rate notes due 2016 (0.444%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	[2]	$ 700	700
Interest rate		0.444%
Notes Payable [Member] | Floating rate notes due 2019 (0.772%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	[2]	$ 400	400
Interest rate		0.772%
Notes Payable [Member] | Floating rate notes due 2021 (0.892%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	[2]	$ 400	400
Interest rate		0.892%
Notes Payable [Member] | Floating rate notes due 2022 (0.952%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	[2]	$ 350	0
Interest rate		0.952%
Notes Payable [Member] | Amortizing Bank Loan due 2018 (1.172%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	[2]	$ 110	0
Interest rate		1.172%
Debentures [Member] | 8.625% debentures due 2032 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 147	147
Interest rate		8.625%
Debentures [Member] | 8.625 % debentures due 2031 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 108	107
Interest rate		8.625%
Debentures [Member] | 8 % debentures due 2032 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 74	74
Interest rate		8.00%
Debentures [Member] | 9.75 % debentures due 2020 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 54	54
Interest rate		9.75%
Debentures [Member] | 8.875 % debentures due 2021 [Member]
Debt Instrument [Line Items]
Long-term debt instruments		$ 40	40
Interest rate		8.875%
Medium-term Notes [Member] | Medium-term notes, maturing from 2021 to 2038 (5.83%) [Member]
Debt Instrument [Line Items]
Long-term debt instruments	[1]	$ 38	$ 38
Interest rate		5.975%
Corporate Bond Securities [Member]
Debt Instrument [Line Items]
Debt issued				$ 5,000	$ 6,000

[1] Weighted-average interest rate at December 31, 2015.

[2] Interest rate at December 31, 2015.